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Re: [Linux-cluster] Problem in clvmd/dlm_recoverd

On 20/11/2008, at 8:37 AM, Brandon Young wrote:

Could you please share the parameters you tuned, and perhaps a brief explanation of your thinking? I have hideously slow backups, too, and haven't been successful in improving it through tuning.


On Wed, Nov 19, 2008 at 3:56 PM, Tom Lanyon <tom netspot com au> wrote:
After tuning some GFS parameters yesterday, last night's backup ran without a hitch! :)

I changed settings to try and reduce the amount of locks held on the backup server. I was assuming that as the application servers were still trying to access the GFS mountpoint, they had to wait until the locks held on the backup server demoted and this was causing the applications to hang.

I tuned glock_purge (it was disabled, I set it to 50%) and reduced demote_secs to 100; I also turned on fast_statfs and increased the number of statfs_slots to try and increase backup performance (in case it does a lot of statfs calls).

However, after further testing we encountered more instability issues. Performance was greatly improved, but we were still finding storage locking up on multiple cluster nodes.

This seems to be more of an issue with GNBD (on which we're running GFS) rather than GFS itself. When the lock up happens, all machines continue to run but any commands that reference the GNBD export hang (ie, lvm, df, mount).

I haven't been able to confirm this since GNBD isn't giving me any errors, but we're still investigating.


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