[Linux-cluster] Unformatting a GFS cluster disk
christopher barry
Christopher.Barry at qlogic.com
Fri Apr 4 03:23:27 UTC 2008
On Sun, 2008-03-30 at 14:54 -0500, Wendy Cheng wrote:
snip...
> In general, GFS backup from Linux side during run time has been a pain,
> mostly because of its slowness and the process has to walk thru the
> whole filesystem to read every single file that ends up accumulating
> non-trivial amount of cached glocks and memory. For a sizable filesystem
> (say in TBs range like yours), past experiences have shown that after
> backup(s), the filesystem latency can go up to an unacceptable level
> unless its glocks are trimmed. There is a tunable specifically written
> for this purpose (glock_purge - introduced via RHEL 4.5 ) though.
What should I be setting glock_purge to?
snip...
> The thinking here is to leverage the embedded Netapp copy-on-write
> feature to speed up the backup process with reasonable disk space
> requirement. The snapshot volume and the cloned lun shouldn't take much
> disk space and we can turn on gfs readahead and glock_purge tunables
> with minimum interruptions to the original gfs volume. The caveat here
> is GFS-mounting the cloned lun - for one, gfs itself at this moment
> doesn't allow mounting of multiple devices that have the same filesystem
> identifiers (the -t value you use during mkfs time e.g.
> "cluster-name:filesystem-name") on the same node - but it can be fixed
> (by rewriting the filesystem ID and lock protocol - I will start to test
> out the described backup script and a gfs kernel patch next week). Also
> as any tape backup from linux host, you should not expect an image of
> gfs mountable device (when retrieving from tape) - it is basically a
> collection of all files residing on the gfs filesystem when the backup
> events take places.
>
> Will the above serve your need ? Maybe other folks have (other) better
> ideas ?
This sounds exactly like what I can use - and it's got to be useful for
everyone with a NetApp and gfs. Thanks for doing this! Let me know how I
can help.
Regards,
-C
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