Moab Workload Manager®

A.5  Case Study: Multi-Queue Cluster with QOS and Charge Rates

A 160 node, single processor Linux cluster is to be used to support various organizations within an enterprise.  The system should allow a user to request improved job turnaround time in exchange for a higher charge rate.  A portion of the system must be reserved for small development jobs at all times. 

Management desires the following queue structure:

QueueName      Nodes        MaxWallTime   Priority     ChargeRate
-----------------------------------------------------------------
Test            <=16            0:30:00        100             1x
Serial             1            2:00:00         10             1x
Serial-Long        1           24:00:00         10             2x
Short           2-16            4:00:00         10             1x
Short-Long      2-16           24:00:00         10             2x
Med            17-64            8:00:00         20             1x
Med-Long       17-64           24:00:00         20             2x
Large          65-80           24:00:00         50             2x
LargeMem           1            8:00:00         10             4x

For charging, management has decided to charge by job walltime since the nodes will not be shared.  Management has also dictated that 16 of the single processor nodes should be dedicated to running small jobs requiring 16 or fewer nodes.  Management has also decided that it would like to allow only serial jobs to run on the large memory nodes and would like to charge these jobs at a rate of 4x.  There are no constraints on the remaining nodes. 

This site has goals which are focused more on a supplying a straightforward queue environment to the end users than on maximizing the scheduling performance of the system.  The Moab configuration has the primary purpose of faithfully reproducing the queue constraints above while maintaining reasonable scheduling performance in the process. 

Since we are using PBS as the resource manager, this should be a pretty straightforward process.  It will involve setting up an allocations manager to handle charging, configuring queue priorities, and creating a system reservation to manage the 16 processors dedicated to small jobs, and another for managing the large memory nodes. 

First, the queue structure must be configured.  The best place to handle this is via the PBS configuration.  The qmgr command can be used to set up the nine queues described above.  PBS supports the node and walltime constraints as well as the queue priorities.  Moab will honor queue priorities configured within PBS.  Alternatively, these priorities can be specified directly within the Moab fs.cfg file for resource managers which do not support this capability. 

We will be using QBank to handle all allocations and so, will want to configure the the "per class charge rates" there.  Note that QBank 2.9 or higher is required for per class charge rate support. 

Now, two reservations are needed.  The first reservation will be for the 16 small memory nodes.  It should only allow node access to jobs requesting up to 16 processors.  In this environment, this is probably most easily accomplished with a reservation class ACL containing the queues which allow 1 - 16 node jobs. 

The commands mdiag -s and mdiag -r can be used to examine the standing reservations and all reservations in more detail.  The mdiag -c command can be used to examine and verify class/queue information.  The mshow command may also be used to display information about a class/queue, job, and reservation. 

Moab supports intelligent scheduling across a wide variety of existing queue types.  This intelligence allows administrators to charge for access to priority resources in a very flexible manner.  Moab will work seamlessly with other software products to implement the desired behavior.