[OmniOS-discuss] [discuss] background snapshot destruction impact

[Richard Elling]

Hi Tobias,
comments below…

On Dec 21, 2013, at 5:15 AM, Tobias Oetiker <tobi at oetiker.ch> wrote:

> I am running omnios r151008 on a recent box with 3gig SAS disks
> arranged in a raidz2 pool.
> 
> I have this 7TB filesystem where I have my zimbra server store its
> backups.  The backup-sets are highly redundant, so for a time I had
> deduplication turned on to great effect, but as the size of the
> backup-sets grew, I ran out of ram and performance on the system
> became realy bad. So I turned deduplication of. Performance for
> newly written data is fine again.
> 
> The other day, I destroyed a bunch of old snapshots on this
> filesysem. Thanks to background destruction this did not realy take
> a long time. But now as background destruction is progressing, the
> system remains very slugish when doing io on the pool where
> the destruction is taking place.
> 
> I put up some graphs and raw data on
> 
>  http://tobi.oetiker.ch/background-destruction/
> 
> to show the state of things.
> 
> My Questions:
> 
> a) would it be faster to send/receive the content of the
>   deduplicated filesystem to a new non deduplicated
>   and then destroy the entire filesystem (not the pool).
> 
> b) is there a way to monitor progress on the background
>   destruction?
> 
> c) shouldn't the smarter write throttle change
>   https://github.com/illumos/illumos-gate/commit/69962b5647e4a8b9b14998733b765925381b727e
>   have helped with this by makeing zfs do its internal things
>   with a lower priority.

Yes, but the default zfs_vdev_max_pending remains at 10. Once
the I/Os are sent to disk, there is no priority scheduling. You
should consider lowering zfs_vdev_max_pending to allow the ZIO
scheduler to do a better job of rescheduling the more important
I/Os.
 — richard

> 
> cheers
> tobi
> 
> 
> -- 
> Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
> http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900
> 
> 
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