Snapshot performance

[Kris Kennaway]

On Fri, Sep 01, 2006 at 04:06:01PM -0700, Skylar Thompson wrote:
> Kris Kennaway wrote:
> > On Fri, Sep 01, 2006 at 11:08:51AM -0700, Paul Lathrop wrote:
> >   
> >> Hi all,
> >>
> >> We're working on deploying a new mail server on FreeBSD 6.1-STABLE. One
> >> of the major selling points was the ability to take filesystem snapshots
> >> in order to make backups from a consistent filesystem on such a
> >> high-traffic system. Unfortunately, when I take a snapshot, performance
> >> slows to a crawl - to the point where the system stops responding to
> >> network requests (ping, SMTP, etc.). Also, the snapshot takes 10-15
> >> minutes to complete.
> >>
> >> Is this a typical situation? Will I need to schedule downtime for
> >> backups in spite of this nifty new feature? Am I doing something wrong?
> >>     
> >
> > Time depends on the size of the filesystem - but you are correct that
> > snapshots were not designed with performance in mind (rather, to speed
> > up booting after an unclean shutdown by removing the need to wait for
> > fsck).
> >
> > Kris
> >   
> Are there plans to improve performance of snapshots? Using the
> freebsd-snapshot port to link FS snapshots to the automounter is pretty
> nifty, but it does kill I/O performance while that's in progress as the
> OP mentioned.

Unfortunately I don't think anyone is working on it.  The closest
thing on the horizon is ZFS support which does feature
high-performance snapshots.  This is still a way off though.

Kris
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