SCSI RDMA Protocol (SRP) Target driver for Linux
=================================================

The SRP Target driver is designed to work directly on top of the
OpenFabrics OFED-1.x software stack (http://www.openfabrics.org) or
the Infiniband drivers in the Linux kernel tree
(http://www.kernel.org). The SRP target driver also interfaces with
the generic SCSI target mid-level driver called SCST
(http://scst.sourceforge.net).

How-to run
-----------

A. On srp target machine
1. Please refer to SCST's README for loading scst driver and its
dev_handlers drivers (scst_disk, scst_vdisk block or file IO mode, nullio, ...)

Example 1: working with real back-end scsi disks
a. modprobe scst
b. modprobe scst_disk
c. cat /proc/scsi_tgt/scsi_tgt

ibstor00:~ # cat /proc/scsi_tgt/scsi_tgt
Device (host:ch:id:lun or name)                             Device handler
0:0:0:0                                                     dev_disk
4:0:0:0                                                     dev_disk
5:0:0:0                                                     dev_disk
6:0:0:0                                                     dev_disk
7:0:0:0                                                     dev_disk

Now you want to exclude the first scsi disk and expose the last 4 scsi disks as
IB/SRP luns for I/O
echo "add 4:0:0:0 0" >/proc/scsi_tgt/groups/Default/devices
echo "add 5:0:0:0 1" >/proc/scsi_tgt/groups/Default/devices
echo "add 6:0:0:0 2" >/proc/scsi_tgt/groups/Default/devices
echo "add 7:0:0:0 3" >/proc/scsi_tgt/groups/Default/devices

Example 2: working with VDISK FILEIO mode (using md0 device and file 10G-file)
a. modprobe scst
b. modprobe scst_vdisk
c. echo "open vdisk0 /dev/md0" > /proc/scsi_tgt/vdisk/vdisk
d. echo "open vdisk1 /10G-file" > /proc/scsi_tgt/vdisk/vdisk
e. echo "add vdisk0 0" >/proc/scsi_tgt/groups/Default/devices
f. echo "add vdisk1 1" >/proc/scsi_tgt/groups/Default/devices

Example 3: working with VDISK BLOCKIO mode (using md0 device, sda, and cciss/c1d0)
a. modprobe scst
b. modprobe scst_vdisk
c. echo "open vdisk0 /dev/md0 BLOCKIO" > /proc/scsi_tgt/vdisk/vdisk
d. echo "open vdisk1 /dev/sda BLOCKIO" > /proc/scsi_tgt/vdisk/vdisk
e. echo "open vdisk2 /dev/cciss/c1d0 BLOCKIO" > /proc/scsi_tgt/vdisk/vdisk
f. echo "add vdisk0 0" >/proc/scsi_tgt/groups/Default/devices
g. echo "add vdisk1 1" >/proc/scsi_tgt/groups/Default/devices
h. echo "add vdisk2 2" >/proc/scsi_tgt/groups/Default/devices

2. modprobe ib_srpt


B. On initiator machines you can manually do the following steps:
1. modprobe ib_srp
2. ibsrpdm -c (to discover new SRP target)
3. echo <new target info> > /sys/class/infiniband_srp/srp-mthca0-1/add_target
4. fdisk -l (will show new discovered scsi disks)

Example:
Assume that you use port 1 of first HCA in the system ie. mthca0

[root@lab104 ~]# ibsrpdm -c -d /dev/infiniband/umad0
id_ext=0002c90200226cf4,ioc_guid=0002c90200226cf4,
dgid=fe800000000000000002c90200226cf5,pkey=ffff,service_id=0002c90200226cf4
[root@lab104 ~]# echo id_ext=0002c90200226cf4,ioc_guid=0002c90200226cf4,
dgid=fe800000000000000002c90200226cf5,pkey=ffff,service_id=0002c90200226cf4 >
/sys/class/infiniband_srp/srp-mthca0-1/add_target

OR

+ You can edit /etc/infiniband/openib.conf to load srp driver and srp HA daemon
automatically ie. set SRP_LOAD=yes, and SRPHA_ENABLE=yes
+ To set up and use high availability feature you need dm-multipath driver
and multipath tool
+ Please refer to OFED-1.x SRP's user manual for more in-details instructions
on how-to enable/use HA feature

To minimize QUEUE_FULL conditions, you can apply scst_increase_max_tgt_cmds
patch from SRPT package from http://sourceforge.net/project/showfiles.php?group_id=110471


Performance notes
-----------------

In some cases, for instance working with SSD devices, which consume 100%
of a single CPU load for data transfers in their internal threads, to
maximize IOPS it can be needed to assign for those threads dedicated
CPUs using Linux CPU affinity facilities. No IRQ processing should be
done on those CPUs. Check that using /proc/interrupts. See taskset
command and Documentation/IRQ-affinity.txt in your kernel's source tree
for how to assign CPU affinity to tasks and IRQs.

The reason for that is that processing of coming commands in SIRQ context
can be done on the same CPUs as SSD devices' threads doing data
transfers. As the result, those threads won't receive all the CPU power
and perform worse.

Alternatively to CPU affinity assignment, you can try to enable SRP
target's internal thread. It will allows Linux CPU scheduler to better
distribute load among available CPUs. To enable SRP target driver's
internal thread you should load ib_srpt module with parameter
"thread=1".


Send questions about this driver to scst-devel@lists.sourceforge.net, CC:
Vu Pham <vuhuong@mellanox.com> and Bart Van Assche <bvanassche@acm.org>.