doc/html/reservations.shtml

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<h1>Resource Reservation Gude</h1>

<p>SLURM verstion 2.0 has the ability to reserve resources for jobs
being executed by select users and/or select bank accounts.
A resource reservation identifies the nodes of a resource reservation 
and a time period during which the reservation is available.
Note that resource reservations are not compatable with SLURM's
gang scheduler plugin since the termination time of running jobs
is not possible to accurately predict.</p>

<p>Reservations can be created, updated, or destroyed only by user root
or the configured <i>SlurmUser</i> using the <i>scontrol</i> command. 
The <i>scontrol</i>, <i>smap</i> and <i>sview</i> commands can be used
to view reservations. 
The man pages for the various commands contain details.</p>

<p>Note for users of Maui or Moab schedulers: <br>
Maui and Moab are not integrated with SLURM's resource reservation system,
but should use their own advanced reservation system.</p>

<h2>Reservation Creation</h2>

<p>One common mode of operation for a reservation would be to reserve
an entire computer at a particular time for a system down time.
The example below shows the creation of a full-system reservation 
at 16:00 hours on 6 February and lasting for 120 minutes. 
The "maint" flag is used to identify the reservation for accounting 
purposes as system maintenance. 
The "ignore_jobs" flag is used to indicate that we can ignore currently 
running jobs when creating this reservation. 
By default, only nodes which are not expected to have a running job
at the start time can be reserved (the time limit of all running 
jobs will have been reached).
In this case we can manually cancel the running jobs as needed 
to perform system maintenance.
As the reservation time approaches, 
only jobs that can complete by the reservation time will be 
initiated.</p>
<pre>
$ scontrol create reservation starttime=2009-02-06T16:00:00 \
   duration=120 user=root flags=maint,ignore_jobs nodes=ALL
Reservation created: root_4

$ scontrol show reservation
ReservationName=root_4 StartTime=2009-02-06T16:00:00 
   EndTime=2009-02-06T18:00:00 Duration=120
   Nodes=ALL NodeCnt=20 Features=(null) PartitionName=(null)
   Flags=MAINT,SPEC_NODES,IGNORE_JOBS Users=root Accounts=(null)
</pre>

<p>Another mode of operation would be to reserve specific nodes
for an indefinite period in order to study problems on those 
nodes. This could also be accomplished using a SLURM partition
specifically for this purpose, but that would fail to capture
the maintenance nature of their use.</p>
<pre>
$ scontrol create reservation user=root starttime=now \
   duration=infinite flags=maint nodes=sun000
Reservation created: root_5

$ scontrol show res
ReservationName=root_5 StartTime=2009-02-04T16:22:57 
   EndTime=2009-02-04T16:21:57 Duration=4294967295
   Nodes=sun000 NodeCnt=1 Features=(null) PartitionName=(null)
   Flags=MAINT,SPEC_NODES Users=root Accounts=(null)
</pre>

<p>Our final example is to reserve ten nodes in the default 
SLURM partition starting at noon and with a duration of 60 
minutes occuring daily. The reservation will be available
only to users alan and brenda.</p>
<pre>
$ scontrol create reservation user=alan,brenda \
   starttime=noon duration=60 flags=daily nodecnt=10
Reservation created: alan_6

$ scontrol show res
ReservationName=alan_6 StartTime=2009-02-05T12:00:00 
   EndTime=2009-02-05T13:00:00 Duration=60
   Nodes=sun[000-003,007,010-013,017] NodeCnt=10 
   Features=(null) PartitionName=pdebug Flags=DAILY
   Users=alan,brenda Accounts=(null)
</pre>

<p>Note that specific nodes to be associated with the reservation are
made immediately after creation of the reservation. This permits
users to stage files to the nodes in preparation for use during the
reservation. Note that the reservation creation request can also 
identify the partition from which to select the nodes or _one_
feature that every selected node must contain.</p>

<p>Reservations must not overlap, with the exception of 
maintenance mode as described below. They must either include 
different nodes or operate at different times. If specific nodes
are not specified when a reservation is created, SLURM will 
automatically select nodes to avoid overlap and insure that
the selected nodes are available when the reservation begins.
For ease of system maintenance, you can create a reservation
with the "maint" flag that overlaps existing reservations.
This permits an administrator to easily create a maintenance 
reservation for an entire cluster without needing to remove 
or reschedule pre-existing reservations.</p>

<h2>Reservation Use</h2>

<p>The reservation create response includes the reservation's name.
This name is automatically generated by SLURM based upon the first
user or account name and a numeric suffix. In order to use the 
reservation, the job submit request must explicitly specify that
reservation name. The job must be contained completely within the
named reservation. The job will be cancelled after the reservation 
reaches its EndTime. If letting the job continue execution after
the reservation EndTime, a configuration option <i>ResvOverRun</i>
can be set to control how long the job can continue execution.</p>
<pre>
$ sbatch --reservation=alan_6 -N4 my.script
sbatch: Submitted batch job 65540
</pre>

<h2>Reservation Modification</h2>

<p>Reservations can be modified by user root as desired. 
For example their duration could be altered or the users
granted access changed as shown below:</p>
<pre>
$ scontrol update ReservationName=root_4 \
   duration=150 users=admin
Reservation updated.

bash-3.00$ scontrol show ReservationName=root_4
ReservationName=root_4 StartTime=2009-02-06T16:00:00 
   EndTime=2009-02-06T18:30:00 Duration=150
   Nodes=ALL NodeCnt=20 Features=(null) 
   PartitionName=(null) Flags=MAINT,SPEC_NODES
   Users=jette Accounts=(null)
</pre>

<h2>Reservation Deletion</h2>

<p>Reservations are automatically purged after their end time. 
They may also be manually deleted as shown below. 
Note that a reservation can not be deleted while there are
jobs running in it.</p>
<pre>
$ scontrol delete ReservationName=alan_6
</pre>

<h2>Reservation Accounting</h2>

<p>Jobs executed within a reservation are accounted for using the appropriate
user and bank account. If resources within a reservation are not used, those 
resources will be accounted for as being used by all users or bank accounts
associated with the reservation on an equal basis (e.g. if two users are
eligible to use a reservation and neither does, each user will be reported 
to have used half of the reserved resources).</p>

<h2>Future Work</h2>

<p>Several enhancements are anticipated at some point in the future.
<ol>
<li>The automatic selection of nodes for a reservation create request may be
sub-optimal in terms of locality (for optimized application communication).</li>
<li> The feature specification in the reservation creation request should be 
made more flexible to accept multiple features with AND or OR operators.</li> 
</ol>


<p style="text-align: center;">Last modified 15 June 2009</p>

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