Snapshot usage guidelines (to avoid stability issues)

[Kostik Belousov]

On Wed, Jun 20, 2007 at 06:26:26PM +0200, Espen Skoglund wrote:
> Hi,
> 
> A couple of days ago I decided to start using snapshots on my system.
> Knowing that the functionality has been available for quite some time
> now I (apparently wrongly) assumed that it was ready for production
> use.  My bad.
> 
> My system, a 6-STABLE from week and a half ago, uses two 250GB
> gstriped disks and has about 4-5 snapshots on one 215GB UFS partiton.
> This morning I learned that things had gone terribly wrong during some
> nightly cronjobs, hanging the whole system.  Suspecting that snapshots
> were the culprit I soon learned after some investigation that the
> snapshot functionality wasn't nearly as stable as I had hoped for.
> 
> Looking at PRs and mailing lists there seems to be mainly two
> outstanding stability issues with snapshots: a) snapshotted fs running
> full, and b) deleting large amount of files on an fs with multiple
> snapshots.  The former issue, while certainly annoying, one could be
> able to work around.  The latter issue, on the other hand, seems more
> like a definite show stopper.
> 
> Am I right in inferring that the two above cases are main issues with
> snaphots at this time, or are there other known gotchas that I have to
> look out for.
About the issue b). Are you system sources before or after 2007-06-11
10:53:48 UTC ? Or simply show me the version of sys/ufs/ffs/ffs_snapshot.c.

If it is less then 1.103.2.24, see developers handbook for instruction on
reporting deadlocks.

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