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[Linux-cluster] Backup of a GFS2 volume


I've a Red Hat 5.7 2-node cluster for electronic mail services where the mailboxes (maildir format)
are stored on GFS2 volume. The volume contains about 7500000 files for ~740 GB of disk space
occupation. Previously the mailboxes were on a GFS1 volume, and I migrated to GFS2 when we changed
the SAN storage system.

Due to incremental backups that have become extremely slow (about 41-42H) after the migration from
GFS to GFS2, I checked the configuration/tuning of the cluster and volume mount options, with the
help of Red Hat support, but the optimizations (<gfs_controld plock_rate_limit="0"/>, mount with
noatime and nodiratime) don't have significantly accelerated the incremental backups.

So I tried another backup strategy, using the snaphot feature of our SAN storage system, doing
backups outside the cluster environment. I use the snapshots of the GSF2 on another server (also
with RHEL 5.7) mounting the volume as a local (not clustered) filesystem:

/var/mailboxes type gfs2 (rw,noatime,nodiratime,lockproto=lock_nolock,localflocks,localcaching)

The duration of full backups are slightly better (from 24-25H to 21-22H of duration) and the
incremental backup are "acceptable" (about 9H). But the speed is still low in comparison to backups
of Ext3 filesystems, particularly for incremental backups.

I've notice that the glocks are still used, also when I mount a snapshot of the mailbox GFS2
partition as a local filesystem:

# mount -t gfs2 /dev/mapper/posta_mbox_disk_vg-posta_mbox_disk_lvol1 /var/mailboxes -o
# time cp -Rp /var/mailboxes/prova* /var/tmp/test/

real	2m5.648s
user	0m0.311s
sys	0m13.243s
# rm -Rf /var/tmp/test/*
# time cp -Rp /var/mailboxes/prova* /var/tmp/test/

real	0m10.946s
user	0m0.254s
sys	0m10.634s

# cat /proc/slabinfo | grep gloc
gfs2_glock         35056  35064    424    9    1 : tunables   54   27    8 : slabdata   3896   3896

Is there a way to exclude the use of the glocks, or them are necessary to access the partition, even
if mounted as local filesystem?


Davide Brunato

Davide Brunato
Sistema Informatico SISSA: http://sis.sissa.it
via Bonomea 265 - 34136 Trieste - Italy
tel: +39-040-3787538  e-mail: brunato sissa it

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