mystery: lock up after fs dump

[Jeremy Chadwick]

On Wed, Jun 04, 2008 at 06:33:45PM +0300, Andriy Gapon wrote:
> on 04/06/2008 18:23 Kostik Belousov said the following:
> > On Wed, Jun 04, 2008 at 06:07:47PM +0300, Andriy Gapon wrote:
> [snip]
> >> dumps are done on live filesystems using -L.
> [snip]
> >> 4. both systems have gjournal support (on 6.X it is added via a
> >> "non-official" patch), there are gjournaled filesystems on both systems
> >> and they are dumped.
> > 
> > Do you use snapshots on the gjournaled fs ? I believe this is problematic.
> 
> Yes, I do via dump -L. I don't otherwise (no mksnap_ffs).
> I had some thoughts about that.
> But... I remember discussing this on geom list and I think pjd said that
> this should work and also it worked for me flawlessly except for that
> one moment.
> BTW, those filesystems are mounted like the following:
> ufs, asynchronous, local, noatime, gjournal
> This is to say that I do not mix gjournal and softupdates, which is also
> possible (at least not prohibited).

I haven't seen hard system lock-ups when using dump (the -L on UFS2
systems is implied, but you're not using softupdates, so maybe it's not
implied on such), but I have seen all I/O on the system lock up hard
until the actual snapshot finishes being taken.

I mentioned this a while ago on -stable (not sure; I can dig up the
thread), and was told that essentially this is a known problem with
snapshots on UFS2, and that the problem over time gets worse and worse.

Ultimately I stopped using dump and switched to rsync.

-- 
| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |