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[Linux-cluster] OOM failures with GFS, NFS and Samba on a cluster with RHEL3-AS

I have been experiencing OOM failures (followed by reboots) on a cluster running Dell PowerEdge 1860's (dual-proc, 4GB RAM) with RHEL3-AS with all current updates.

The system is configured as a two-member cluster, running GFS 6.0.2-25 (RH SRPM) and cluster services 1.2.16-1 (also RH SRPM). My original testing went fine with the cluster, including service fail-over and all that stuff (only one lock_gulmd, so if the master goes down, the world explodes--but I expected that).

Use seemed to be okay, but there weren't a whole lot of users. Recently, a project wanted to serve some data from their space in GFS via their own machine. We mounted their space via NFS from the cluster, and they serve their data via samba from their machine. Shortly thereafter, two things happened: more people started to access the data, and the cluster machines started to crash. The symptoms are that free memory drops extremely quickly (sometimes more than 3GB disappears in less than two minutes). Load average usually goes up quickly (when I can see it). NFS processes are normally at the top of top, along with kswapd. At some point, around this time, the kernel starts to spit out OOM messages and it starts to kill bunches of processes. The machine eventually reboots itself and comes back up cleanly.

Space of outages seems to be dependent on how many people are using the system, but I've also seen the machine go down when the backup system runs a few backups on the machine. One of the things I've noticed, though, is that the backup system doesn't actually cause the machine to crash if the system has been recently rebooted, and memory usage returns to normal after the backup is finished. Memory usage usually does NOT return to completely normal after the gigabytes of memory become used (when that happens, the machine will sit there and keep running for a while with only 20MB or less free, until something presumably tries to use that memory and the machine flips out). That is the only time I've seen the backup system cause the system to crash--after it has endured significant usage during the day and there are 20MB or less free.

I'll usually get a call from the culprits telling me that they were copying either a) lots of files or b) large files to the cluster.

Any ideas here? Anything I can look at to tune?


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