[Linux-cluster] Problem with write performance

Arturo Gonzalez Ferrer arturogf at gmail.com
Mon Jan 18 15:05:15 UTC 2010

Thank you F. Javier,

But the problem is that we use gfs2, and it does not seem to have these
tunables as you can read at:

So, we do not have the chance to test it...I think.

It would be very nice to, at least, know what is this problem related to.


2010/1/18 Pena, Francisco Javier <francisco_javier.pena at roche.com>

> Hello Arturo,
> The following Red Hat KB article may be useful in your case:
> http://kbase.redhat.com/faq/docs/DOC-6533 . The glock_purge and
> demote_secs tunables have been quite useful to us in some cases, and your
> case looks similar.
> The only drawback of this method is that you will need to write a script
> somewhere to set the tunables, as they are not persistent.
> Regards,
> Javier
> ________________________________________
> From: linux-cluster-bounces at redhat.com [mailto:
> linux-cluster-bounces at redhat.com] On Behalf Of Arturo Gonzalez Ferrer
> Sent: Saturday, January 16, 2010 9:35 PM
> To: linux clustering
> Subject: [Linux-cluster] Problem with write performance
> Hello,
> We've set up recently a rhel 5.4 cluster of 3 nodes for a Moodle
> high-availability website, where the sessions and data are share in a GFS2
> volume.
> We found that, while the read performance have been constantly good, there
> is a problem with writes, as the system decrease its peformance after some
> conditions. We think that it can be related with our backup procedure:
> We do an NFS export of the GFS2 volume from one of the nodes, so that we
> can backup the volume every night externally, from a veritas backup client.
> After that, we find next morning that the write performance has decreased a
> lot, so that it is practically unusable for some big files and for the
> operation of cloning an existing course (zip, unzip the data of the course
> in a new folder). After some experiments with the writes and clone
> operations, we have found a way that improve the issue, but we think that
> there should be a better way. What we did was to add the next entry to
> crontab in every node:
> 0-59/10 * * * * sync; echo 3 > /proc/sys/vm/drop_caches
> So that the lock caches are cleaned every ten minutes, as we didn't notice
> that it affects badly to the performance of the system, and effectivily, it
> improves the write performance somehow, at least making it usable.
> Do you think this could be an option? Do you have a better explanation for
> it? Any other ideas what could we do?
> We have been since then having problems with apache service, being stopped
> sometimes (not very offen) in one of the nodes. I think that it could be
> related to this maintenance of the vm caches... but I'm not sure.
> Best regards,
> Arturo.
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