[zfs-discuss] One dataset per user?

Arne Jansen
2010-06-20T16:26:45Z

Roy Sigurd Karlsbakk wrote:
>
> I have read people are having problems with lengthy boot times with lots of
datasets. We''re planning to do extensive snapshotting on this system,
so there might be close to a hundred snapshots per dataset, perhaps more. With
200 users and perhaps 10-20 shared department datasets, the number of
filesystems, snapshots included, will be around 20k or more.

In my experience the boot time mainly depends on the number of datasets, not the
number of snapshots. 200 datasets is fairly easy (we have >7000, but did
some boot-time tuning).

>
> Will trying such a setup be betting on help from some god, or is it doable?
The box we''re planning to use will have 48 gigs of memory and about 1TB
L2ARC (shared with SLOG, we just use some slices for that).

Try. The main problem with having many snapshots is the time used for zfs list,
because it has to scrape all the information from disk, but with having so much
RAM/L2ARC that shouldn''t be a problem here.
Another thing to consider is the frequency with which you plan to take the snap-
shots and if you want individual schedules for each dataset. Taking a snapshot
is a heavy-weight operation as it terminates the current txg.

Btw, what did you plan to use as L2ARC/slog?

--Arne



>
> Vennlige hilsener / Best regards
>
> roy
> --
> Roy Sigurd Karlsbakk
> (+47) 97542685
> roy at karlsbakk.net
> http://blogg.karlsbakk.net/
> --
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