UFS2 Snapshots in 6.1-Beta4 - Confirmed Problems

[John Kozubik]

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 at kozubik.com - http://www.kozubik.com