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Regarding the jobs failing around 2am

This entry was posted by on Wednesday, 24 October, 2012 at

We received multiple reports of jobs getting killed around 2:00am. After further investigation, we have found the cause and made the corrections required to prevent this from happening again. Here’s a detailed explanation of what caused the job failures:

Each individual machine in PACE, including workstations in some cases, has an OS-software stack that is maintained by a single-sourced service called GTSWD. During maintenance periods we often use the GTSWD service to push-out new OS updates, firmware updates, and system service updates.

One of the updates we pushed out during the last maintenance window was a new panfs client, which is responsible for mounting the /scratch filesystem. The process used to update the panfs client came in two stages:

#1 initiate the client installation under the assumption that the node was free (this was a valid assumption at that time because this was being done during the maintenance window).

#2 replace the process that did the client installation with another update process that would first check to see if the change had already been made, but more importantly, would not make the assumption that the node was free.

On some of the compute nodes, #2 didn’t not get applied, and so every day at 2am since maintenance day, process #1 has been attempting to umount and remount /scratch, causing the failure of several user jobs. The reason #2 did not get applied, is because the GTSWD service-source is now completely overwhelmed by the number of PACE nodes that we now have trying to use it, and had not been able to automatically apply the updates to a small subset of our nodes.

In terms of this particular problem, we have manually updated all the RHEL5 nodes that were still using process #1; that will stop any more jobs that use RHEL5 queues from getting killed at 2am. In terms of the capacity problem, we’re going to be adding more capacity to the GTSWD service so that it can support all of the PACE nodes. On the RHEL6 nodes we’ve updated the execution instruction sets on our distribution system such that, when updated, they will not attempt to use process #1.

We are sorry for the time this has cost you, and also for not correcting the problem sooner. The failure rate of GTSWD has been historically very low, and thus is usually one of the very last things we look at when trying to determine the source of a problem.

 

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