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Date:      Tue, 21 Mar 2006 12:07:04 -0800 (PST)
From:      John Kozubik <john@kozubik.com>
To:        Kris Kennaway <kris@obsecurity.org>
Cc:        freebsd-fs@freebsd.org, jroberson@chesapeake.net, tegge@freebsd.org
Subject:   Re: UFS2 Snapshots in 6.1-Beta4 - Confirmed Problems
Message-ID:  <20060321120255.I55763@kozubik.com>
In-Reply-To: <20060321194904.GA20959@xor.obsecurity.org>
References:  <20060320224313.O55763@kozubik.com> <20060321184127.GA19204@xor.obsecurity.org> <20060321113923.I55763@kozubik.com> <20060321194904.GA20959@xor.obsecurity.org>

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On Tue, 21 Mar 2006, Kris Kennaway wrote:

> > > > This next one is complicated, and I haven't submitted a PR for it yet, but
> > > > I believe it is quite serious for reasons I will expand on below.
> > > >
> > > > The problem is:  If you completely fill a filesystem (109% usage in `df`
> > > > on most systems) that has a snapshot on it, the system becomes very
> > > > unresponsive - all interactive and disk response lags terribly and,
> > > > although the system is not hung, it is in many cases unusable.
> > >
> > > Yes :-( This will probably not be fixable in time for 6.1, but
> > > hopefully it will be addressed in the future.  FYI, the system may
> > > also panic in this situation.
> >
> >
> > Because my original description of this behavior was so vague, I was going
> > to try to reproduce it again with more details, however it sounds like you
> > have already witnessed this and know more about it than I do.
> >
> > Is that true ?  Can I skip a few hours of trying to reproduce this ?
>
> Yes, I'm easily able to reproduce it, and I'm told that fixing it will
> require fairly extensive work & testing.


Ok.  Please contact me when that testing is needed as I am happy to help.

Can I use this time to suggest that in all testing of snapshot related
issues, that multiple (preferably 4+) snapshots per filesystem are used ?
Many of the problems either do not manifest themselves, or are not as
pronounced with only one snapshot running.

Thanks.

-----
John Kozubik - john@kozubik.com - http://www.kozubik.com



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