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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<refentry id="re-drbdconf">
<refentryinfo>
<date>6 May 2011</date>
<productname>DRBD</productname>
<productnumber>8.4.0</productnumber>
</refentryinfo>
<refmeta>
<refentrytitle>drbd.conf</refentrytitle>
<manvolnum>5</manvolnum>
<refmiscinfo class="manual">Configuration Files</refmiscinfo>
</refmeta>
<refnamediv>
<refname>drbd.conf</refname>
<refpurpose>Configuration file for DRBD's devices <indexterm significance="normal">
<primary>drbd.conf</primary>
</indexterm></refpurpose>
</refnamediv>
<refsect1>
<title>Introduction</title>
<para>The file <option>/etc/drbd.conf</option> is read by <option>drbdadm</option>.</para>
<para>The file format was designed as to allow to have a verbatim copy of the file on both
nodes of the cluster. It is highly recommended to do so in order to keep your configuration
manageable. The file <option>/etc/drbd.conf</option> should be the same on both nodes of the
cluster. Changes to <option>/etc/drbd.conf</option> do not apply immediately.</para>
<para>By convention the main config contains two include statements. The first one includes
the file <option>/etc/drbd.d/global_common.conf</option>, the second one all file with a
<option>.res</option> suffix.</para>
<para><example>
<title>A small example.res file</title>
<programlisting format="linespecific">resource r0 {
net {
protocol C;
cram-hmac-alg sha1;
shared-secret "FooFunFactory";
}
disk {
resync-rate 10M;
}
on alice {
volume 0 {
device minor 1;
disk /dev/sda7;
meta-disk internal;
}
address 10.1.1.31:7789;
}
on bob {
volume 0 {
device minor 1;
disk /dev/sda7;
meta-disk internal;
}
address 10.1.1.32:7789;
}
}</programlisting>
</example>In this example, there is a single DRBD resource (called r0) which uses protocol C
for the connection between its devices. It contains a single volume which runs on host
<replaceable>alice</replaceable> uses <replaceable>/dev/drbd1</replaceable> as devices for its
application, and <replaceable>/dev/sda7</replaceable> as low-level storage for the data. The
IP addresses are used to specify the networking interfaces to be used. An eventually running
resync process should use about 10MByte/second of IO bandwidth. This sync-rate statement is
valid for volume 0, but would also be valid for further volumes. In this example it assigns
full 10MByte/second to each volume.</para>
<para>There may be multiple resource sections in a single drbd.conf file. For more examples,
please have a look at the
<ulink url="http://www.drbd.org/users-guide/"><citetitle>DRBD User's Guide</citetitle></ulink>.</para>
</refsect1>
<refsect1>
<title>File Format</title>
<para>The file consists of sections and parameters. A section begins with a keyword, sometimes
an additional name, and an opening brace (<quote>{</quote>). A section ends with a closing
brace (<quote>}</quote>. The braces enclose the parameters.</para>
<para>section [name] { parameter value; [...] }</para>
<para>A parameter starts with the identifier of the parameter followed by whitespace. Every
subsequent character is considered as part of the parameter's value. A special case are
Boolean parameters which consist only of the identifier. Parameters are terminated by a
semicolon (<quote>;</quote>).</para>
<para>Some parameter values have default units which might be overruled by K, M or G. These
units are defined in the usual way (K = 2^10 = 1024, M = 1024 K, G = 1024 M).</para>
<para>Comments may be placed into the configuration file and must begin with a hash sign
(<quote>#</quote>). Subsequent characters are ignored until the end of the line.</para>
<refsect2>
<title>Sections</title>
<variablelist>
<varlistentry>
<term xml:id="skip"><option>skip</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>skip</secondary>
</indexterm> Comments out chunks of text, even spanning more than one line.
Characters between the keyword <option>skip</option> and the opening brace
(<quote>{</quote>) are ignored. Everything enclosed by the braces is skipped. This
comes in handy, if you just want to comment out some '<option>resource [name]
{...}</option>' section: just precede it with '<option>skip</option>'.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="global"><option>global</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>global</secondary>
</indexterm> Configures some global parameters. Currently only
<option>minor-count</option>, <option>dialog-refresh</option>,
<option>disable-ip-verification</option> and <option>usage-count</option> are allowed
here. You may only have one global section, preferably as the first section.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="common"><option>common</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>common</secondary>
</indexterm> All resources inherit the options set in this section. The common
section might have a <option>startup</option>, a <option>options</option>, a
<option>handlers</option>, a <option>net</option> and a <option>disk</option>
section.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="resource"><option>resource <replaceable>name</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>resource</secondary>
</indexterm> Configures a DRBD resource. Each resource section needs to have two (or
more) <option>on <replaceable>host</replaceable></option> sections and may have a
<option>startup</option>, a <option>options</option>, a <option>handlers</option>, a
<option>net</option> and a <option>disk</option> section. It might contain
<option>volume</option>s sections.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="on"><option>on <replaceable>host-name</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>on</secondary>
</indexterm> Carries the necessary configuration parameters for a DRBD device of the
enclosing resource. <replaceable>host-name</replaceable> is mandatory and must match
the Linux host name (uname -n) of one of the nodes. You may list more than one host
name here, in case you want to use the same parameters on several hosts (you'd have to
move the IP around usually). Or you may list more than two such sections.
<programlisting format="linespecific"> resource r1 {
protocol C;
device minor 1;
meta-disk internal;
on alice bob {
address 10.2.2.100:7801;
disk /dev/mapper/some-san;
}
on charlie {
address 10.2.2.101:7801;
disk /dev/mapper/other-san;
}
on daisy {
address 10.2.2.103:7801;
disk /dev/mapper/other-san-as-seen-from-daisy;
}
}
</programlisting>See also the <option>floating</option> section keyword. Required statements in
this section: <option>address</option> and <option>volume</option>. Note for backward
compatibility and convenience it is valid to embed the statements of a single volume
directly into the host section.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="volume"><option>volume <replaceable>vnr</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>volume</secondary>
</indexterm> Defines a volume within a connection. The minor numbers of a replicated
volume might be different on different hosts, the volume number
(<replaceable>vnr</replaceable>) is what groups them together. Required parameters in
this section: <option>device</option>, <option>disk</option>,
<option>meta-disk</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="stacked-on-top-of"><option>stacked-on-top-of <replaceable>resource</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>stacked-on-top-of</secondary>
</indexterm> For a stacked DRBD setup (3 or 4 nodes), a
<option>stacked-on-top-of</option> is used instead of an <option>on</option> section.
Required parameters in this section: <option>device</option> and
<option>address</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="floating"><option>floating <replaceable>AF addr:port</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>on</secondary>
</indexterm> Carries the necessary configuration parameters for a DRBD device of the
enclosing resource. This section is very similar to the <option>on</option> section.
The difference to the <option>on</option> section is that the matching of the host
sections to machines is done by the IP-address instead of the node name. Required
parameters in this section: <option>device</option>, <option>disk</option>,
<option>meta-disk</option>, all of which
<emphasis>may</emphasis> be inherited from the resource section, in which case you may
shorten this section down to just the address identifier. <programlisting
format="linespecific"> resource r2 {
protocol C;
device minor 2;
disk /dev/sda7;
meta-disk internal;
# short form, device, disk and meta-disk inherited
floating 10.1.1.31:7802;
# longer form, only device inherited
floating 10.1.1.32:7802 {
disk /dev/sdb;
meta-disk /dev/sdc8;
}
}
</programlisting></para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="s-disk"><option>disk</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>disk</secondary>
</indexterm> This section is used to fine tune DRBD's properties in respect to the
low level storage. Please refer to <citerefentry>
<refentrytitle>drbdsetup</refentrytitle>
<manvolnum>8</manvolnum>
</citerefentry> for detailed description of the parameters. Optional parameters:
<option>on-io-error</option>, <option>size</option>, <option>fencing</option>,
<option>disk-barrier</option>, <option>disk-flushes</option>,
<option>disk-drain</option>, <option>md-flushes</option>,
<option>max-bio-bvecs</option>, <option>resync-rate</option>,
<option>resync-after</option>, <option>al-extents</option>, <option>al-updates</option>,
<option>c-plan-ahead</option>, <option>c-fill-target</option>,
<option>c-delay-target</option>, <option>c-max-rate</option>,
<option>c-min-rate</option>, <option>disk-timeout</option>,
<option>discard-zeroes-if-aligned</option>,
<option>rs-discard-granularity</option>,
<option>read-balancing</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="net"><option>net</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>net</secondary>
</indexterm> This section is used to fine tune DRBD's properties. Please refer to
<citerefentry>
<refentrytitle>drbdsetup</refentrytitle>
<manvolnum>8</manvolnum>
</citerefentry> for a detailed description of this section's parameters. Optional
parameters: <option>protocol</option>, <option>sndbuf-size</option>,
<option>rcvbuf-size</option>, <option>timeout</option>, <option>connect-int</option>,
<option>ping-int</option>, <option>ping-timeout</option>,
<option>max-buffers</option>, <option>max-epoch-size</option>,
<option>ko-count</option>, <option>allow-two-primaries</option>,
<option>cram-hmac-alg</option>, <option>shared-secret</option>,
<option>after-sb-0pri</option>, <option>after-sb-1pri</option>,
<option>after-sb-2pri</option>, <option>data-integrity-alg</option>,
<option>no-tcp-cork</option>, <option>on-congestion</option>,
<option>congestion-fill</option>, <option>congestion-extents</option>,
<option>verify-alg</option>, <option>use-rle</option>,
<option>csums-alg</option>,
<option>socket-check-timeout</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="startup"><option>startup</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>startup</secondary>
</indexterm> This section is used to fine tune DRBD's properties. Please refer to
<citerefentry>
<refentrytitle>drbdsetup</refentrytitle>
<manvolnum>8</manvolnum>
</citerefentry> for a detailed description of this section's parameters. Optional
parameters: <option>wfc-timeout</option>, <option>degr-wfc-timeout</option>,
<option>outdated-wfc-timeout</option>, <option>wait-after-sb</option>,
<option>stacked-timeouts</option> and <option>become-primary-on</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="options"><option>options</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>options</secondary>
</indexterm> This section is used to fine tune the behaviour of the resource object.
Please refer to <citerefentry>
<refentrytitle>drbdsetup</refentrytitle>
<manvolnum>8</manvolnum>
</citerefentry> for a detailed description of this section's parameters. Optional
parameters: <option>cpu-mask</option>, and
<option>on-no-data-accessible</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="handlers"><option>handlers</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>handlers</secondary>
</indexterm> In this section you can define handlers (executables) that are started
by the DRBD system in response to certain events. Optional parameters:
<option>pri-on-incon-degr</option>, <option>pri-lost-after-sb</option>,
<option>pri-lost</option>, <option>fence-peer</option> (formerly oudate-peer),
<option>local-io-error</option>, <option>initial-split-brain</option>,
<option>split-brain</option>, <option>before-resync-target</option>,
<option>after-resync-target</option>.</para>
<para>The interface is done via environment variables:<itemizedlist>
<listitem>
<para><option>DRBD_RESOURCE</option> is the name of the resource</para>
</listitem>
<listitem>
<para><option>DRBD_MINOR</option> is the minor number of the DRBD device, in
decimal.</para>
</listitem>
<listitem>
<para><option>DRBD_CONF</option> is the path to the primary configuration file;
if you split your configuration into multiple files (e.g. in
<option>/etc/drbd.conf.d/</option>), this will not be helpful.</para>
</listitem>
<listitem>
<para><option>DRBD_PEER_AF</option> , <option>DRBD_PEER_ADDRESS</option> ,
<option>DRBD_PEERS</option> are the address family (e.g. <option>ipv6</option>),
the peer's address and hostnames.</para>
</listitem>
</itemizedlist> <option>DRBD_PEER</option> is deprecated.</para>
<para>Please note that not all of these might be set for all handlers, and that some
values might not be useable for a <option>floating</option> definition.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect2>
<refsect2>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term xml:id="minor-count"><option>minor-count <replaceable>count</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>minor-count</secondary>
</indexterm><replaceable>count</replaceable> may be a number from 1 to 1048575.</para>
<para><replaceable>Minor-count</replaceable> is a sizing hint for DRBD. It helps to
right-size various memory pools. It should be set in the in the same order of
magnitude than the actual number of minors you use. Per default the module loads with
11 more resources than you have currently in your config but at least 32.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="dialog-refresh"><option>dialog-refresh <replaceable>time</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>dialog-refresh</secondary>
</indexterm><replaceable>time</replaceable> may be 0 or a positive number.</para>
<para>The user dialog redraws the second count every <replaceable>time</replaceable>
seconds (or does no redraws if <replaceable>time</replaceable> is 0). The default
value is 1.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="disable-ip-verification"><option>disable-ip-verification</option></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>disable-ip-verification</secondary>
</indexterm>
<para>Use <replaceable>disable-ip-verification</replaceable> if, for some obscure
reasons, drbdadm can/might not use <option>ip</option> or <option>ifconfig</option> to
do a sanity check for the IP address. You can disable the IP verification with this
option.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="udev-always-use-vnr"><option>udev-always-use-vnr</option></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>udev-always-use-vnr</secondary>
</indexterm>
<para>When udev asks drbdadm for a list of device related symlinks,
drbdadm would suggest symlinks with differing naming conventions,
depending on whether the resource has explicit
<literal>volume VNR { }</literal> definitions,
or only one single volume with the implicit volume number 0:
<programlisting><![CDATA[
# implicit single volume without "volume 0 {}" block
DEVICE=drbd<minor>
SYMLINK_BY_RES=drbd/by-res/<resource-name>
# explicit volume definition: volume VNR { }
DEVICE=drbd<minor>
SYMLINK_BY_RES=drbd/by-res/<resource-name>/VNR
]]></programlisting>
</para>
<para>If you define this parameter in the global section,
drbdadm will always add the <literal>.../VNR</literal> part,
and will not care for whether the volume definition was implicit or explicit.
</para>
<para>For legacy backward compatibility, this is off by default,
but we do recommend to enable it.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="usage-count"><option>usage-count <replaceable>val</replaceable></option></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>usage-count</secondary>
</indexterm>
<para>Please participate in
<ulink url="http://usage.drbd.org"><citetitle>DRBD's online usage counter</citetitle></ulink>.
The most convenient way to do so is to set
this option to <option>yes</option>. Valid options are: <option>yes</option>,
<option>no</option> and <option>ask</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="protocol"><option>protocol <replaceable>prot-id</replaceable></option></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>protocol</secondary>
</indexterm>
<para>On the TCP/IP link the specified <replaceable>protocol</replaceable> is used.
Valid protocol specifiers are A, B, and C.</para>
<para>Protocol A: write IO is reported as completed, if it has reached local disk and
local TCP send buffer.</para>
<para>Protocol B: write IO is reported as completed, if it has reached local disk and
remote buffer cache.</para>
<para>Protocol C: write IO is reported as completed, if it has reached both local and
remote disk.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="device"><option>device <replaceable>name</replaceable> minor
<replaceable>nr</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>device</secondary>
</indexterm> The name of the block device node of the resource being described. You
must use this device with your application (file system) and you must not use the low
level block device which is specified with the <option>disk</option> parameter.</para>
<para>One can ether omit the <replaceable>name</replaceable> or <option>minor</option>
and the <replaceable>minor number</replaceable>. If you omit the
<replaceable>name</replaceable> a default of /dev/drbd<replaceable>minor</replaceable>
will be used.</para>
<para>Udev will create additional symlinks in /dev/drbd/by-res and
/dev/drbd/by-disk.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="disk"><option>disk <replaceable>name</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>disk</secondary>
</indexterm> DRBD uses this block device to actually store and retrieve the data.
Never access such a device while DRBD is running on top of it. This also holds true
for <citerefentry>
<refentrytitle>dumpe2fs</refentrytitle>
<manvolnum>8</manvolnum>
</citerefentry> and similar commands.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="address"><option>address <replaceable>AF addr:port</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>address</secondary>
</indexterm> A resource needs one <replaceable>IP</replaceable> address per device,
which is used to wait for incoming connections from the partner device respectively to
reach the partner device. <replaceable>AF</replaceable> must be one of
<option>ipv4</option>, <option>ipv6</option>, <option>ssocks</option> or
<option>sdp</option> (for compatibility reasons <option>sci</option> is an alias for
<option>ssocks</option>). It may be omited for IPv4 addresses. The actual IPv6 address
that follows the <option>ipv6</option> keyword must be placed inside brackets:
<literal moreinfo="none">ipv6 [fd01:2345:6789:abcd::1]:7800</literal>.</para>
<para>Each DRBD resource needs a TCP <replaceable>port</replaceable> which is used to
connect to the node's partner device. Two different DRBD resources may not use the
same <replaceable>addr:port</replaceable> combination on the same node.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="meta-disk"><option>meta-disk internal</option></term>
<term><option>meta-disk <replaceable>device</replaceable></option></term>
<term><option>meta-disk <replaceable>device</replaceable> [<replaceable>index</replaceable>]</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>meta-disk</secondary>
</indexterm> Internal means that the last part of the backing device is used to
store the meta-data. The size of the meta-data is computed based on the size of the
device.</para>
<para>When a <replaceable>device</replaceable> is specified, either with or without an
<replaceable>index</replaceable>, DRBD stores the meta-data on this device. Without
<replaceable>index</replaceable>, the size of the meta-data is determined by the size
of the data device. This is usually used with LVM, which allows to have many variable
sized block devices. The meta-data size is 36kB + Backing-Storage-size / 32k, rounded up
to the next 4kb boundary. (Rule of the thumb: 32kByte per 1GByte of storage, rounded up
to the next MB.)</para>
<para>When an <replaceable>index</replaceable> is specified, each index number refers to
a fixed slot of meta-data of 128 MB, which allows a maximum data size of 4 TiB. This way,
multiple DBRD devices can share the same meta-data device. For example, if /dev/sde6[0]
and /dev/sde6[1] are used, /dev/sde6 must be at least 256 MB big. Because of the hard size
limit, use of meta-disk indexes is discouraged.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="on-io-error"><option>on-io-error <replaceable>handler</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>on-io-error</secondary>
</indexterm><replaceable>handler</replaceable> is taken, if the lower level device
reports io-errors to the upper layers.</para>
<para><replaceable>handler</replaceable> may be <option>pass_on</option>,
<option>call-local-io-error</option> or <option>detach.</option></para>
<para><option>pass_on</option>: The node downgrades the disk status to inconsistent, marks the
erroneous block as inconsistent in the bitmap and retries the IO on the remote node.</para>
<para><option>call-local-io-error</option>: Call the handler script
<option>local-io-error</option>.</para>
<para><option>detach</option>: The node drops its low level device, and continues in
diskless mode.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="fencing"><option>fencing <replaceable>fencing_policy</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>fencing</secondary>
</indexterm> By <option>fencing</option> we understand preventive measures to avoid
situations where both nodes are primary and disconnected (AKA split brain).</para>
<para>Valid fencing policies are:</para>
<variablelist>
<varlistentry>
<term xml:id="dont-care"><option>dont-care</option></term>
<listitem>
<para>This is the default policy. No fencing actions are taken.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="resource-only"><option>resource-only</option></term>
<listitem>
<para>If a node becomes a disconnected primary, it tries to fence the peer's
disk. This is done by calling the <option>fence-peer</option> handler. The
handler is supposed to reach the other node over alternative communication paths
and call '<option>drbdadm outdate res</option>' there.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="resource-and-stonith"><option>resource-and-stonith</option></term>
<listitem>
<para>If a node becomes a disconnected primary, it freezes all its IO operations
and calls its fence-peer handler. The fence-peer handler is supposed to reach
the peer over alternative communication paths and call 'drbdadm outdate res'
there. In case it cannot reach the peer it should stonith the peer. IO is
resumed as soon as the situation is resolved. In case your handler fails, you
can resume IO with the <option>resume-io</option> command.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="disk-barrier"><option>disk-barrier</option></term>
<term xml:id="disk-flushes"><option>disk-flushes</option></term>
<term xml:id="disk-drain"><option>disk-drain</option></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>disk-barrier</secondary>
</indexterm>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>disk-flushes</secondary>
</indexterm>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>disk-drain</secondary>
</indexterm>
<para>DRBD has four implementations to express write-after-write dependencies to its
backing storage device. DRBD will use the first method that is supported by the
backing storage device and that is not disabled. By default the <emphasis>flush</emphasis>
method is used.</para>
<para>Since drbd-8.4.2 <option>disk-barrier</option> is disabled by default
because since linux-2.6.36 (or 2.6.32 RHEL6) there is no reliable way to determine if queuing
of IO-barriers works. <emphasis>Dangerous</emphasis> only enable if you are
told so by one that knows for sure.</para>
<para>When selecting the method you should not only base your decision on the
measurable performance. In case your backing storage device has a volatile write cache
(plain disks, RAID of plain disks) you should use one of the first two. In case your
backing storage device has battery-backed write cache you may go with option 3.
Option 4 (disable everything, use "none") <emphasis>is dangerous</emphasis>
on most IO stacks, may result in write-reordering, and if so,
can theoretically be the reason for data corruption, or disturb
the DRBD protocol, causing spurious disconnect/reconnect cycles.
<emphasis>Do not use</emphasis> <option>no-disk-drain</option>.</para>
<para>Unfortunately device mapper (LVM) might not support barriers.</para>
<para>The letter after "wo:" in /proc/drbd indicates with method is currently in use
for a device: <option>b</option>, <option>f</option>, <option>d</option>,
<option>n</option>. The implementations are:</para>
<variablelist>
<varlistentry>
<term>barrier</term>
<listitem>
<para>The first requires that the driver of the backing storage device support
barriers (called 'tagged command queuing' in SCSI and 'native command queuing'
in SATA speak). The use of this method can be enabled by setting the
<option>disk-barrier</option> options to <option>yes</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>flush</term>
<listitem>
<para>The second requires that the backing device support disk flushes (called
'force unit access' in the drive vendors speak). The use of this method can be
disabled setting <option>disk-flushes</option> to <option>no</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>drain</term>
<listitem>
<para>The third method is simply to let write requests drain before write
requests of a new reordering domain are issued. This was the only implementation
before 8.0.9.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>none</term>
<listitem>
<para>The fourth method is to not express write-after-write dependencies to
the backing store at all, by also specifying <option>no-disk-drain</option>.
This <emphasis>is dangerous</emphasis>
on most IO stacks, may result in write-reordering, and if so,
can theoretically be the reason for data corruption, or disturb
the DRBD protocol, causing spurious disconnect/reconnect cycles.
<emphasis>Do not use</emphasis> <option>no-disk-drain</option>.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="md-flushes"><option>md-flushes</option></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>md-flushes</secondary>
</indexterm>
<para>Disables the use of disk flushes and barrier BIOs when accessing the meta data
device. See the notes on <option>disk-flushes</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="max-bio-bvecs"><option>max-bio-bvecs</option></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>max-bio-bvecs</secondary>
</indexterm>
<para>In some special circumstances the device mapper stack manages to pass BIOs to
DRBD that violate the constraints that are set forth by DRBD's merge_bvec() function
and which have more than one bvec. A known example is: phys-disk -&gt; DRBD -&gt; LVM
-&gt; Xen -&gt; misaligned partition (63) -&gt; DomU FS. Then you might see "bio would
need to, but cannot, be split:" in the Dom0's kernel log.</para>
<para>The best workaround is to proper align the partition within the VM (E.g. start
it at sector 1024). This costs 480 KiB of storage. Unfortunately the default of most
Linux partitioning tools is to start the first partition at an odd number (63).
Therefore most distribution's install helpers for virtual linux machines will end up
with misaligned partitions. The second best workaround is to limit DRBD's max bvecs
per BIO (= <option>max-bio-bvecs</option>) to 1, but that might cost
performance.</para>
<para>The default value of <option>max-bio-bvecs</option> is 0, which means that there
is no user imposed limitation.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<option>disk-timeout</option>
</term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>disk-timeout</secondary>
</indexterm>
<para>If the lower-level device on which a DRBD device stores its data does
not finish an I/O request within the defined
<option>disk-timeout</option>, DRBD treats this as a failure. The
lower-level device is detached, and the device's disk state advances to
Diskless. If DRBD is connected to one or more peers, the failed request
is passed on to one of them.</para>
<para>This option is <emphasis>dangerous and may lead to kernel panic!</emphasis></para>
<para>"Aborting" requests, or force-detaching the disk, is intended for
completely blocked/hung local backing devices which do no longer
complete requests at all, not even do error completions. In this
situation, usually a hard-reset and failover is the only way out.</para>
<para>By "aborting", basically faking a local error-completion,
we allow for a more graceful swichover by cleanly migrating services.
Still the affected node has to be rebooted "soon".</para>
<para>By completing these requests, we allow the upper layers to re-use
the associated data pages.</para>
<para>If later the local backing device "recovers", and now DMAs some data
from disk into the original request pages, in the best case it will
just put random data into unused pages; but typically it will corrupt
meanwhile completely unrelated data, causing all sorts of damage.</para>
<para>Which means delayed successful completion,
especially for READ requests, is a reason to panic().
We assume that a delayed *error* completion is OK,
though we still will complain noisily about it.</para>
<para>The default value of
<option>disk-timeout</option> is 0, which stands for an infinite timeout.
Timeouts are specified in units of 0.1 seconds. This option is available
since DRBD 8.3.12.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="discard-zeroes-if-aligned"><option>discard-zeroes-if-aligned <group choice="req" rep="norepeat">
<arg choice="plain" rep="norepeat">yes</arg>
<arg choice="plain" rep="norepeat">no</arg>
</group></option></term>
<listitem>
<para>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>discard-zeroes-if-aligned</secondary>
</indexterm>
There are several aspects to discard/trim/unmap support on linux
block devices. Even if discard is supported in general, it may fail
silently, or may partially ignore discard requests. Devices also
announce whether reading from unmapped blocks returns defined data
(usually zeroes), or undefined data (possibly old data, possibly
garbage).
</para><para>
If on different nodes, DRBD is backed by devices with differing discard
characteristics, discards may lead to data divergence (old data or
garbage left over on one backend, zeroes due to unmapped areas on the
other backend). Online verify would now potentially report tons of
spurious differences. While probably harmless for most use cases
(fstrim on a file system), DRBD cannot have that.
</para><para>
To play safe, we have to disable discard support, if our local backend
(on a Primary) does not support "discard_zeroes_data=true". We also have to
translate discards to explicit zero-out on the receiving side, unless
the receiving side (Secondary) supports "discard_zeroes_data=true",
thereby allocating areas what were supposed to be unmapped.
</para><para>
There are some devices (notably the LVM/DM thin provisioning) that are
capable of discard, but announce discard_zeroes_data=false. In the case of
DM-thin, discards aligned to the chunk size will be unmapped, and
reading from unmapped sectors will return zeroes. However, unaligned
partial head or tail areas of discard requests will be silently ignored.
</para><para>
If we now add a helper to explicitly zero-out these unaligned partial
areas, while passing on the discard of the aligned full chunks, we
effectively achieve discard_zeroes_data=true on such devices.
</para><para>
Setting <option>discard-zeroes-if-aligned</option> to <option>yes</option>
will allow DRBD to use discards, and to announce discard_zeroes_data=true,
even on backends that announce discard_zeroes_data=false.
</para><para>
Setting <option>discard-zeroes-if-aligned</option> to <option>no</option>
will cause DRBD to always fall-back to zero-out on the receiving side,
and to not even announce discard capabilities on the Primary,
if the respective backend announces discard_zeroes_data=false.
</para><para>
We used to ignore the discard_zeroes_data setting completely. To not
break established and expected behaviour, and suddenly cause fstrim on
thin-provisioned LVs to run out-of-space instead of freeing up space,
the default value is <option>yes</option>.
</para><para>
This option is available since 8.4.7.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<option>read-balancing <replaceable>method</replaceable></option>
</term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>read-balancing</secondary>
</indexterm>
<para>
The supported <replaceable>methods</replaceable> for load balancing of
read requests are <option>prefer-local</option>, <option>prefer-remote</option>,
<option>round-robin</option>, <option>least-pending</option>,
<option>when-congested-remote</option>, <option>32K-striping</option>,
<option>64K-striping</option>, <option>128K-striping</option>,
<option>256K-striping</option>, <option>512K-striping</option>
and <option>1M-striping</option>.</para>
<para> The default value of is <option>prefer-local</option>.
This option is available since 8.4.1.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="rs-discard-granularity">
<option>rs-discard-granularity <replaceable>byte</replaceable></option>
</term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>rs-discard-granularity</secondary>
</indexterm>
<para>
When <option>rs-discard-granularity</option> is set to a non zero, positive
value then DRBD tries to do a resync operation in requests of this size.
In case such a block contains only zero bytes on the sync source node,
the sync target node will issue a discard/trim/unmap command for
the area.</para>
<para>The value is constrained by the discard granularity of the backing
block device. In case <option>rs-discard-granularity</option> is not a
multiplier of the discard granularity of the backing block device DRBD
rounds it up. The feature only gets active if the backing block device
reads back zeroes after a discard command.</para>
<para> The default value of is 0. This option is available since 8.4.7.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="sndbuf-size"><option>sndbuf-size <replaceable>size</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>sndbuf-size</secondary>
</indexterm><replaceable>size</replaceable> is the size of the TCP socket send
buffer. The default value is 0, i.e. autotune. You can specify smaller or larger
values. Larger values are appropriate for reasonable write throughput with protocol A
over high latency networks. Values below 32K do not make sense. Since 8.0.13 resp.
8.2.7, setting the <replaceable>size</replaceable> value to 0 means that the kernel
should autotune this.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="rcvbuf-size"><option>rcvbuf-size <replaceable>size</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>rcvbuf-size</secondary>
</indexterm><replaceable>size</replaceable> is the size of the TCP socket receive
buffer. The default value is 0, i.e. autotune. You can specify smaller or larger
values. Usually this should be left at its default. Setting the
<replaceable>size</replaceable> value to 0 means that the kernel should autotune
this.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="timeout"><option>timeout <replaceable>time</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>timeout</secondary>
</indexterm> If the partner node fails to send an expected response packet within
<replaceable>time</replaceable> tenths of a second, the partner node is considered
dead and therefore the TCP/IP connection is abandoned. This must be lower than
<replaceable>connect-int</replaceable> and <replaceable>ping-int</replaceable>. The
default value is 60 = 6 seconds, the unit 0.1 seconds.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="connect-int"><option>connect-int <replaceable>time</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>connect-int</secondary>
</indexterm> In case it is not possible to connect to the remote DRBD device
immediately, DRBD keeps on trying to connect. With this option you can set the time
between two retries. The default value is 10 seconds, the unit is 1 second.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="ping-int"><option>ping-int <replaceable>time</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>ping-int</secondary>
</indexterm> If the TCP/IP connection linking a DRBD device pair is idle for more
than <replaceable>time</replaceable> seconds, DRBD will generate a keep-alive packet
to check if its partner is still alive. The default is 10 seconds, the unit is 1
second.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="ping-timeout"><option>ping-timeout <replaceable>time</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>ping-timeout</secondary>
</indexterm> The time the peer has time to answer to a keep-alive packet. In case
the peer's reply is not received within this time period, it is considered as dead.
The default value is 500ms, the default unit are tenths of a second.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="max-buffers"><option>max-buffers <replaceable>number</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>max-buffers</secondary>
</indexterm>
Limits the memory usage per DRBD minor device on the receiving side,
or for internal buffers during resync or online-verify.
Unit is PAGE_SIZE, which is 4 KiB on most systems.
The minimum possible setting is hard coded to 32 (=128 KiB).
These buffers are used to hold data blocks while they are written to/read from disk.
To avoid possible distributed deadlocks on congestion, this setting is used
as a throttle threshold rather than a hard limit. Once more than max-buffers
pages are in use, further allocation from this pool is throttled.
You want to increase max-buffers if you cannot saturate the IO backend on the
receiving side.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="ko-count"><option>ko-count <replaceable>number</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>ko-count</secondary>
</indexterm> In case the secondary node fails to complete a single write request for
<replaceable>count</replaceable> times the <replaceable>timeout</replaceable>, it is
expelled from the cluster. (I.e. the primary node will kill and restart the connection.)
To disable this feature, you should explicitly set it to 0; defaults may change between versions.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="max-epoch-size"><option>max-epoch-size <replaceable>number</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>max-epoch-size</secondary>
</indexterm> The highest number of data blocks between two write barriers. If you
set this smaller than 10, you might decrease your performance.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="allow-two-primaries"><option>allow-two-primaries</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>allow-two-primaries</secondary>
</indexterm> With this option set you may assign the primary role to both nodes. You
only should use this option if you use a shared storage file system on top of DRBD. At
the time of writing the only ones are: OCFS2 and GFS. If you use this option with any
other file system, you are going to crash your nodes and to corrupt your data!</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="unplug-watermark"><option>unplug-watermark <replaceable>number</replaceable></option></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>unplug-watermark</secondary>
</indexterm>
<para>
This setting has no effect with recent kernels that use explicit on-stack
plugging (upstream Linux kernel 2.6.39, distributions may have backported).
</para>
<para>When the number of pending write requests on the standby (secondary) node
exceeds the <option>unplug-watermark</option>, we trigger the request processing of
our backing storage device. Some storage controllers deliver better performance with
small values, others deliver best performance when the value is set to the same value
as max-buffers, yet others don't feel much effect at all.
Minimum 16, default 128, maximum 131072.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="cram-hmac-alg"><option>cram-hmac-alg</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>cram-hmac-alg</secondary>
</indexterm> You need to specify the HMAC algorithm to enable peer authentication at
all. You are strongly encouraged to use peer authentication. The HMAC algorithm will
be used for the challenge response authentication of the peer. You may specify any
digest algorithm that is named in <option>/proc/crypto</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="shared-secret"><option>shared-secret</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>shared-secret</secondary>
</indexterm> The shared secret used in peer authentication. May be up to 64
characters. Note that peer authentication is disabled as long as no
<option>cram-hmac-alg</option> (see above) is specified.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="after-sb-0pri"><option>after-sb-0pri </option> <replaceable>policy</replaceable></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>after-sb-0pri</secondary>
</indexterm>
<para>possible policies are:</para>
<variablelist>
<varlistentry>
<term xml:id="disconnect"><option>disconnect</option></term>
<listitem>
<para>No automatic resynchronization, simply disconnect.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="discard-younger-primary"><option>discard-younger-primary</option></term>
<listitem>
<para>Auto sync from the node that was primary before the split-brain situation
happened.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="discard-older-primary"><option>discard-older-primary</option></term>
<listitem>
<para>Auto sync from the node that became primary as second during the
split-brain situation.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="discard-zero-changes"><option>discard-zero-changes</option></term>
<listitem>
<para>In case one node did not write anything since the split brain became
evident, sync from the node that wrote something to the node that did not write
anything. In case none wrote anything this policy uses a random decision to
perform a "resync" of 0 blocks. In case both have written something this policy
disconnects the nodes.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="discard-least-changes"><option>discard-least-changes</option></term>
<listitem>
<para>Auto sync from the node that touched more blocks during the split brain
situation.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="discard-node-NODENAME"><option>discard-node-NODENAME</option></term>
<listitem>
<para>Auto sync to the named node.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="after-sb-1pri"><option>after-sb-1pri </option> <replaceable>policy</replaceable></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>after-sb-1pri</secondary>
</indexterm>
<para>possible policies are:</para>
<variablelist>
<varlistentry>
<term xml:id="sb1-disconnect"><option>disconnect</option></term>
<listitem>
<para>No automatic resynchronization, simply disconnect.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="consensus"><option>consensus</option></term>
<listitem>
<para>Discard the version of the secondary if the outcome of the
<option>after-sb-0pri</option> algorithm would also destroy the current
secondary's data. Otherwise disconnect.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="sb1-violently-as0p"><option>violently-as0p</option></term>
<listitem>
<para>Always take the decision of the <option>after-sb-0pri</option> algorithm,
even if that causes an erratic change of the primary's view of the data. This is
only useful if you use a one-node FS (i.e. not OCFS2 or GFS) with the
<option>allow-two-primaries</option> flag, <emphasis>AND</emphasis> if you
really know what you are doing. This is <emphasis>DANGEROUS and MAY CRASH YOUR
MACHINE</emphasis> if you have an FS mounted on the primary node.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="discard-secondary"><option>discard-secondary</option></term>
<listitem>
<para>Discard the secondary's version.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="sb1-call-pri-lost-after-sb"><option>call-pri-lost-after-sb</option></term>
<listitem>
<para>Always honor the outcome of the <option>after-sb-0pri </option> algorithm.
In case it decides the current secondary has the right data, it calls the
"pri-lost-after-sb" handler on the current primary.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="after-sb-2pri"><option>after-sb-2pri </option> <replaceable>policy</replaceable></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>after-sb-2pri</secondary>
</indexterm>
<para>possible policies are:</para>
<variablelist>
<varlistentry>
<term xml:id="sb2-disconnect"><option>disconnect</option></term>
<listitem>
<para>No automatic resynchronization, simply disconnect.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="sb2-violently-as0p"><option>violently-as0p</option></term>
<listitem>
<para>Always take the decision of the <option>after-sb-0pri</option> algorithm,
even if that causes an erratic change of the primary's view of the data. This is
only useful if you use a one-node FS (i.e. not OCFS2 or GFS) with the
<option>allow-two-primaries</option> flag, <emphasis>AND</emphasis> if you
really know what you are doing. This is <emphasis>DANGEROUS and MAY CRASH YOUR
MACHINE</emphasis> if you have an FS mounted on the primary node.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="sb2-call-pri-lost-after-sb"><option>call-pri-lost-after-sb</option></term>
<listitem>
<para>Call the "pri-lost-after-sb" helper program on one of the machines. This
program is expected to reboot the machine, i.e. make it secondary.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="always-asbp"><option>always-asbp</option></term>
<listitem>
<para>Normally the automatic after-split-brain policies are only used if current
states of the UUIDs do not indicate the presence of a third node.</para>
<para>With this option you request that the automatic after-split-brain policies are
used as long as the data sets of the nodes are somehow related. This might cause a
full sync, if the UUIDs indicate the presence of a third node. (Or double faults led
to strange UUID sets.)</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="rr-conflict"><option>rr-conflict </option> <replaceable>policy</replaceable></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>rr-conflict</secondary>
</indexterm>
<para>This option helps to solve the cases when the outcome of the resync decision is
incompatible with the current role assignment in the cluster.</para>
<variablelist>
<varlistentry>
<term xml:id="rr-disconnect"><option>disconnect</option></term>
<listitem>
<para>No automatic resynchronization, simply disconnect.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="violently"><option>violently</option></term>
<listitem>
<para>Sync to the primary node is allowed, violating the assumption that data on
a block device are stable for one of the nodes. <emphasis>Dangerous, do not
use.</emphasis></para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="call-pri-lost"><option>call-pri-lost</option></term>
<listitem>
<para>Call the <option>pri-lost-after-sb</option> helper
program on one of the machines unless that machine can
demote to secondary. The helper program is expected to
reboot the machine, which brings the node into a secondary
role. Which machine runs the helper program is determined
by the <option>after-sb-0pri</option> strategy.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="data-integrity-alg"><option>data-integrity-alg </option> <replaceable>alg</replaceable></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>data-integrity-alg</secondary>
</indexterm>
<para>DRBD can ensure the data integrity of the user's data on the network by
comparing hash values. Normally this is ensured by the 16 bit checksums in the headers
of TCP/IP packets.</para>
<para>This option can be set to any of the kernel's data digest algorithms. In a
typical kernel configuration you should have at least one of <option>md5</option>,
<option>sha1</option>, and <option>crc32c</option> available. By default this is not
enabled.</para>
<para>See also the notes on data integrity.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="tcp-cork"><option>tcp-cork</option></term>
<listitem>
<indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>tcp-cork</secondary>
</indexterm>
<para>DRBD usually uses the TCP socket option TCP_CORK to hint to the network stack
when it can expect more data, and when it should flush out what it has in its send
queue. It turned out that there is at least one network stack that performs worse when
one uses this hinting method. Therefore we introducted this option. By setting
<option>tcp-cork</option> to <option>no</option> you can disable the setting and
clearing of the TCP_CORK socket option by DRBD.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="on-congestion"><option>on-congestion <replaceable>congestion_policy</replaceable></option></term>
<term xml:id="congestion-fill"><option>congestion-fill <replaceable>fill_threshold</replaceable></option></term>
<term xml:id="congestion-extents"><option>congestion-extents
<replaceable>active_extents_threshold</replaceable></option></term>
<listitem>
<para>By default DRBD blocks when the available TCP send queue becomes full. That
means it will slow down the application that generates the write requests that cause
DRBD to send more data down that TCP connection.</para>
<para>When DRBD is deployed with DRBD-proxy it might be more desirable that DRBD goes
into AHEAD/BEHIND mode shortly before the send queue becomes full. In AHEAD/BEHIND
mode DRBD does no longer replicate data, but still keeps the connection open.</para>
<para>The advantage of the AHEAD/BEHIND mode is that the application is not slowed
down, even if DRBD-proxy's buffer is not sufficient to buffer all write requests. The
downside is that the peer node falls behind, and that a resync will be necessary to
bring it back into sync. During that resync the peer node will have an inconsistent
disk.</para>
<para>Available <replaceable>congestion_policy</replaceable>s are
<option>block</option> and <option>pull-ahead</option>. The default is
<option>block</option>. <replaceable>Fill_threshold</replaceable> might be in the
range of 0 to 10GiBytes. The default is 0 which disables the check.
<replaceable>Active_extents_threshold</replaceable> has the same limits as
<option>al-extents</option>.</para>
<para>The AHEAD/BEHIND mode and its settings are available since DRBD 8.3.10.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="wfc-timeout"><option>wfc-timeout <replaceable>time</replaceable></option></term>
<listitem>
<para>Wait for connection timeout. <indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>wfc-timeout</secondary>
</indexterm> The init script <citerefentry>
<refentrytitle>drbd</refentrytitle>
<manvolnum>8</manvolnum>
</citerefentry> blocks the boot process until the DRBD resources are connected. When
the cluster manager starts later, it does not see a resource with internal
split-brain. In case you want to limit the wait time, do it here. Default is 0, which
means unlimited. The unit is seconds.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="degr-wfc-timeout"><option>degr-wfc-timeout <replaceable>time</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>degr-wfc-timeout</secondary>
</indexterm> Wait for connection timeout, if this node was a degraded cluster. In
case a degraded cluster (= cluster with only one node left) is rebooted, this timeout
value is used instead of wfc-timeout, because the peer is less likely to show up in
time, if it had been dead before. Value 0 means unlimited.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="outdated-wfc-timeout"><option>outdated-wfc-timeout <replaceable>time</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>outdated-wfc-timeout</secondary>
</indexterm> Wait for connection timeout, if the peer was outdated. In case a
degraded cluster (= cluster with only one node left) with an outdated peer disk is
rebooted, this timeout value is used instead of wfc-timeout, because the peer is not
allowed to become primary in the meantime. Value 0 means unlimited.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="wait-after-sb"><option>wait-after-sb</option></term>
<listitem>
<para>By setting this option you can make the init script to continue to wait even if
the device pair had a split brain situation and therefore refuses to connect.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="become-primary-on"><option>become-primary-on <replaceable>node-name</replaceable></option></term>
<listitem>
<para>Sets on which node the device should be promoted to primary role by the init
script. The <replaceable>node-name</replaceable> might either be a host name or the
keyword <option>both</option>. When this option is not set the devices stay in
secondary role on both nodes. Usually one delegates the role assignment to a cluster
manager (e.g. heartbeat).</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="stacked-timeouts"><option>stacked-timeouts</option></term>
<listitem>
<para>Usually <option>wfc-timeout</option> and <option>degr-wfc-timeout</option> are
ignored for stacked devices, instead twice the amount of <option>connect-int</option>
is used for the connection timeouts. With the <option>stacked-timeouts</option>
keyword you disable this, and force DRBD to mind the <option>wfc-timeout</option> and
<option>degr-wfc-timeout</option> statements. Only do that if the peer of the stacked
resource is usually not available or will usually not become primary. By using this
option incorrectly, you run the risk of causing unexpected split brain.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="resync-rate"><option>resync-rate <replaceable>rate</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>resync-rate</secondary>
</indexterm> To ensure a smooth operation of the application on top of DRBD, it is
possible to limit the bandwidth which may be used by background synchronizations. The
default is 250 KB/sec, the default unit is KB/sec. Optional suffixes K, M, G are
allowed.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="use-rle"><option>use-rle</option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>use-rle</secondary>
</indexterm> During resync-handshake, the dirty-bitmaps of the nodes are exchanged
and merged (using bit-or), so the nodes will have the same understanding of which
blocks are dirty. On large devices, the fine grained dirty-bitmap can become large as
well, and the bitmap exchange can take quite some time on low-bandwidth links.</para>
<para>Because the bitmap typically contains compact areas where all bits are unset
(clean) or set (dirty), a simple run-length encoding scheme can considerably reduce
the network traffic necessary for the bitmap exchange.</para>
<para>For backward compatibilty reasons, and because on fast links this possibly does
not improve transfer time but consumes cpu cycles, this defaults to off.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="socket-check-timeout"><option>socket-check-timeout <replaceable>value</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>socket-check-timeout</secondary>
</indexterm> In setups involving a DRBD-proxy and connections that experience a lot of
buffer-bloat it might be necessary to set <option>ping-timeout</option> to an
unusual high value. By default DRBD uses the same value to wait if a newly
established TCP-connection is stable. Since the DRBD-proxy is usually located
in the same data center such a long wait time may hinder DRBD's connect process.
</para>
<para>In such setups <option>socket-check-timeout</option> should be set to
at least to the round trip time between DRBD and DRBD-proxy. I.e. in most
cases to 1.</para>
<para>
The default unit is tenths of a second, the default value is 0 (which causes
DRBD to use the value of <option>ping-timeout</option> instead).
Introduced in 8.4.5.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="resync-after"><option>resync-after <replaceable>res-name</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>resync-after</secondary>
</indexterm> By default, resynchronization of all devices would run in parallel. By
defining a resync-after dependency, the resynchronization of this resource will start
only if the resource <replaceable>res-name</replaceable> is already in connected state
(i.e., has finished its resynchronization).</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="al-extents"><option>al-extents <replaceable>extents</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>al-extents</secondary>
</indexterm> DRBD automatically performs hot area detection. With this parameter you
control how big the hot area (= active set) can get. Each extent marks 4M of the
backing storage (= low-level device). In case a primary node leaves the cluster
unexpectedly, the areas covered by the active set must be resynced upon rejoining of
the failed node. The data structure is stored in the meta-data area, therefore each
change of the active set is a write operation to the meta-data device. A higher number
of extents gives longer resync times but less updates to the meta-data. The default
number of <replaceable>extents</replaceable> is 1237. (Minimum: 7, Maximum:
65534)</para>
<para>
Note that the effective maximum may be smaller, depending on how
you created the device meta data, see also
<citerefentry><refentrytitle>drbdmeta</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
The effective maximum is 919 * (available on-disk activity-log ring-buffer area/4kB -1),
the default 32kB ring-buffer effects a maximum of 6433 (covers more than 25 GiB of data).
We recommend to keep this well within the amount your backend storage
and replication link are able to resync inside of about 5 minutes.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="al-updates"><option>al-updates <group choice="req" rep="norepeat">
<arg choice="plain" rep="norepeat">yes</arg>
<arg choice="plain" rep="norepeat">no</arg>
</group></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>al-updates</secondary>
</indexterm> DRBD's activity log transaction writing makes it possible, that
after the crash of a primary node a partial (bit-map based) resync is
sufficient to bring the node back to up-to-date.
Setting <option>al-updates</option> to <option>no</option> might increase
normal operation performance but causes DRBD to do a full resync
when a crashed primary gets reconnected. The default value is <option>yes</option>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="verify-alg"><option>verify-alg <replaceable>hash-alg</replaceable></option></term>
<listitem>
<para>During online verification (as initiated by the <command
moreinfo="none">verify</command> sub-command), rather than doing a bit-wise
comparison, DRBD applies a hash function to the contents of every block being
verified, and compares that hash with the peer. This option defines the hash algorithm
being used for that purpose. It can be set to any of the kernel's data digest
algorithms. In a typical kernel configuration you should have at least one of
<option>md5</option>, <option>sha1</option>, and <option>crc32c</option> available. By
default this is not enabled; you must set this option explicitly in order to be able
to use on-line device verification.</para>
<para>See also the notes on data integrity.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="csums-alg"><option>csums-alg <replaceable>hash-alg</replaceable></option></term>
<listitem>
<para>A resync process sends all marked data blocks from the source to the destination
node, as long as no <option>csums-alg</option> is given. When one is specified the
resync process exchanges hash values of all marked blocks first, and sends only those
data blocks that have different hash values.</para>
<para>This setting is useful for DRBD setups with low bandwidth links. During the
restart of a crashed primary node, all blocks covered by the activity log are marked
for resync. But a large part of those will actually be still in sync, therefore using
<option>csums-alg</option> will lower the required bandwidth in exchange for CPU
cycles.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="c-plan-ahead"><option>c-plan-ahead <replaceable>plan_time</replaceable></option></term>
<term xml:id="c-fill-target"><option>c-fill-target <replaceable>fill_target</replaceable></option></term>
<term xml:id="c-delay-target"><option>c-delay-target <replaceable>delay_target</replaceable></option></term>
<term xml:id="c-max-rate"><option>c-max-rate <replaceable>max_rate</replaceable></option></term>
<listitem>
<para>The dynamic resync speed controller gets enabled with setting
<replaceable>plan_time</replaceable> to a positive value. It aims to fill the buffers
along the data path with either a constant amount of data
<replaceable>fill_target</replaceable>, or aims to have a constant delay time of
<replaceable>delay_target</replaceable> along the path. The controller has an upper
bound of <replaceable>max_rate</replaceable>.</para>
<para>By <replaceable>plan_time</replaceable> the agility of the controller is
configured. Higher values yield for slower/lower responses of the controller to
deviation from the target value. It should be at least 5 times RTT. For regular data
paths a <replaceable>fill_target</replaceable> in the area of 4k to 100k is
appropriate. For a setup that contains drbd-proxy it is advisable to use
<replaceable>delay_target</replaceable> instead. Only when
<replaceable>fill_target</replaceable> is set to 0 the controller will use
<replaceable>delay_target</replaceable>. 5 times RTT is a reasonable starting value.
<replaceable>Max_rate</replaceable> should be set to the bandwidth available between
the DRBD-hosts and the machines hosting DRBD-proxy, or to the available
disk-bandwidth.</para>
<para>The default value of <replaceable>plan_time</replaceable> is 0, the default unit
is 0.1 seconds. <replaceable>Fill_target</replaceable> has 0 and sectors as default
unit. <replaceable>Delay_target</replaceable> has 1 (100ms) and 0.1 as default unit.
<replaceable>Max_rate</replaceable> has 10240 (100MiB/s) and KiB/s as default
unit.</para>
<para>The dynamic resync speed controller and its settings are available since DRBD
8.3.9.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="c-min-rate"><option>c-min-rate <replaceable>min_rate</replaceable></option></term>
<listitem>
<para>A node that is primary and sync-source has to schedule application IO requests
and resync IO requests. The <replaceable>min_rate</replaceable> tells DRBD use only up
to min_rate for resync IO and to dedicate all other available IO bandwidth to
application requests.</para>
<para>Note: The value 0 has a special meaning. It disables the limitation of resync IO
completely, which might slow down application IO considerably. Set it to a value of 1,
if you prefer that resync IO never slows down application IO.</para>
<para>Note: Although the name might suggest that it is a lower bound for the dynamic
resync speed controller, it is not. If the DRBD-proxy buffer is full, the dynamic
resync speed controller is free to lower the resync speed down to 0, completely
independent of the <option>c-min-rate</option> setting.</para>
<para><replaceable>Min_rate</replaceable> has 4096 (4MiB/s) and KiB/s as default
unit.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="on-no-data-accessible"><option>on-no-data-accessible
<replaceable>ond-policy</replaceable></option></term>
<listitem>
<para>This setting controls what happens to IO requests on a degraded, disk less node
(I.e. no data store is reachable). The available policies are
<option>io-error</option> and <option>suspend-io</option>.</para>
<para>If <replaceable>ond-policy</replaceable> is set to <option>suspend-io</option>
you can either resume IO by attaching/connecting the last lost data storage, or by the
<command moreinfo="none">drbdadm resume-io <replaceable>res</replaceable></command>
command. The latter will result in IO errors of course.</para>
<para>The default is <option>io-error</option>. This setting is available since DRBD
8.3.9.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="cpu-mask"><option>cpu-mask <replaceable>cpu-mask</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>cpu-mask</secondary>
</indexterm> Sets the cpu-affinity-mask for DRBD's kernel threads of this device.
The default value of <replaceable>cpu-mask</replaceable> is 0, which means that DRBD's
kernel threads should be spread over all CPUs of the machine. This value must be given
in hexadecimal notation. If it is too big it will be truncated.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="pri-on-incon-degr"><option>pri-on-incon-degr <replaceable>cmd</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>pri-on-incon-degr</secondary>
</indexterm> This handler is called if the node is primary, degraded and if the
local copy of the data is inconsistent.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="pri-lost-after-sb"><option>pri-lost-after-sb <replaceable>cmd</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>pri-lost-after-sb</secondary>
</indexterm> The node is currently primary, but lost the after-split-brain auto
recovery procedure. As as consequence, it should be abandoned.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="pri-lost"><option>pri-lost <replaceable>cmd</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>pri-lost</secondary>
</indexterm> The node is currently primary, but DRBD's algorithm thinks that it
should become sync target. As a consequence it should give up its primary role.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="fence-peer"><option>fence-peer <replaceable>cmd</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>fence-peer</secondary>
</indexterm> The handler is part of the <option>fencing</option> mechanism. This
handler is called in case the node needs to fence the peer's disk. It should use other
communication paths than DRBD's network link.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="local-io-error"><option>local-io-error <replaceable>cmd</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>local-io-error</secondary>
</indexterm> DRBD got an IO error from the local IO subsystem.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="initial-split-brain"><option>initial-split-brain <replaceable>cmd</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>initial-split-brain</secondary>
</indexterm> DRBD has connected and detected a split brain situation. This handler
can alert someone in all cases of split brain, not just those that go
unresolved.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="split-brain"><option>split-brain <replaceable>cmd</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>split-brain</secondary>
</indexterm> DRBD detected a split brain situation but remains unresolved. Manual
recovery is necessary. This handler should alert someone on duty.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="before-resync-target"><option>before-resync-target <replaceable>cmd</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>before-resync-target</secondary>
</indexterm> DRBD calls this handler just before a resync begins on the node that
becomes resync target. It might be used to take a snapshot of the backing block
device.</para>
</listitem>
</varlistentry>
<varlistentry>
<term xml:id="after-resync-target"><option>after-resync-target <replaceable>cmd</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>after-resync-target</secondary>
</indexterm> DRBD calls this handler just after a resync operation finished on the
node whose disk just became consistent after being inconsistent for the duration of
the resync. It might be used to remove a snapshot of the backing device that was
created by the <option>before-resync-target</option> handler.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect2>
<refsect2>
<title>Other Keywords</title>
<variablelist>
<varlistentry>
<term xml:id="include"><option>include <replaceable>file-pattern</replaceable></option></term>
<listitem>
<para><indexterm significance="normal">
<primary>drbd.conf</primary>
<secondary>include</secondary>
</indexterm> Include all files matching the wildcard pattern
<replaceable>file-pattern</replaceable>. The <option>include</option> statement is
only allowed on the top level, i.e. it is not allowed inside any section.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect2>
</refsect1>
<refsect1 id="data-integrity">
<title>Notes on data integrity</title>
<para>There are two independent methods in DRBD to ensure the integrity of the mirrored data.
The online-verify mechanism and the <option>data-integrity-alg</option> of the
<option>network</option> section.</para>
<para>Both mechanisms might deliver false positives if the user of DRBD modifies the data
which gets written to disk while the transfer goes on. This may happen for swap, or for
certain append while global sync, or truncate/rewrite workloads, and not necessarily poses a
problem for the integrity of the data. Usually when the initiator of the data transfer does
this, it already knows that that data block will not be part of an on disk data structure, or
will be resubmitted with correct data soon enough.</para>
<para>The <option>data-integrity-alg</option> causes the receiving side to log an error about
"Digest integrity check FAILED: Ns +x\n", where N is the sector offset, and x is the size of
the request in bytes. It will then disconnect, and reconnect, thus causing a quick resync. If
the sending side at the same time detected a modification, it warns about "Digest mismatch,
buffer modified by upper layers during write: Ns +x\n", which shows that this was a false
positive. The sending side may detect these buffer modifications immediately after the
unmodified data has been copied to the tcp buffers, in which case the receiving side won't
notice it.</para>
<para>The most recent (2007) example of systematic corruption was an issue with the TCP
offloading engine and the driver of a certain type of GBit NIC. The actual corruption happened
on the DMA transfer from core memory to the card. Since the TCP checksum gets calculated on
the card, this type of corruption stays undetected as long as you do not use either the online
<option>verify</option> or the <option>data-integrity-alg</option>.</para>
<para>We suggest to use the <option>data-integrity-alg</option> only during a pre-production
phase due to its CPU costs. Further we suggest to do online <option>verify</option> runs
regularly e.g. once a month during a low load period.</para>
</refsect1>
<refsect1>
<title>Version</title>
<simpara>This document was revised for version 8.4.0 of the DRBD distribution.</simpara>
</refsect1>
<refsect1>
<title>Author</title>
<simpara>Written by Philipp Reisner <email>philipp.reisner@linbit.com</email> and Lars
Ellenberg <email>lars.ellenberg@linbit.com</email>.</simpara>
</refsect1>
<refsect1>
<title>Reporting Bugs</title>
<simpara>Report bugs to <email>drbd-user@lists.linbit.com</email>.</simpara>
</refsect1>
<refsect1>
<title>Copyright</title>
<simpara>Copyright 2001-2008 LINBIT Information Technologies, Philipp Reisner, Lars Ellenberg.
This is free software; see the source for copying conditions. There is NO warranty; not even
for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.</simpara>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>drbd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>drbddisk</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>drbdsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>drbdmeta</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>drbdadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<ulink url="http://www.drbd.org/users-guide/"><citetitle>DRBD User's Guide</citetitle></ulink>,
<ulink url="http://www.drbd.org/"><citetitle>DRBD web site</citetitle></ulink>
</para>
</refsect1>
</refentry>