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Re: [Linux-cluster] Cluster Project FAQ - GFS tuning section]

Wendell Dingus wrote:
I don't know where that breaking point is but I believe _we've_ stepped
over it.

4-node RHEL3 and GFS6.0 cluster with (2) 2TB filesystems (GULM and no
LVM) versus
3-node RHEL4 (x86_64) and GFS6.1 cluster with (1) 8TB+ filesystem (DLM
and LVM and way faster hardware/disks)

This is a migration from the former to the latter, so quantity/size of
files/dirs is mostly identical. Files being transferred from customer
sites to the old servers never cause more than about 20% CPU load and
that usually (quickly) falls to 1% or less after the initial xfer
begins. The new servers run to 100% where they usually remain until the
transfer completes. The current thinking as far as reason is the same
thing being discussed here.

I was advised of this mailing list posting by a a RH tech from an open
ticket I have on this problem.

The older server has 11million and 13million files respectively across
it's two filesystems. The newer server has about 27million files on it's
one larger filesystem. It appears I'm going to be forced to blow this
away and create multiple smaller filesystems (there is a redundant
backup drive with all the files thank goodness). Unless I hear otherwise
I'm inclined to limit the new RAID to 2TB filesystems max. So as one
filesystem fills up faster than the others I suppose we'll forever be
moving things from one to the other and symlinking it to death. Oh well...
Hi Wendell,

If I understand you correctly, you're having a performance problem here.
If it were me, I guess I'd try some experiments to try to determine where the
bottleneck seems to be.  For example, I'd try temporarily switching to Gulm
locking protocol on the new servers to see if that brings the performance back.

Wendy Cheng has a performance-related bugzilla open right now in GFS:

Your problem might/might not be related.  Would you be willing to test a
patch for her?  I don't know if she has a patch ready to try yet.


Bob Peterson
Red Hat Cluster Suite

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