System hanging during dump

[Jeremy Chadwick]

On Wed, Oct 15, 2008 at 08:48:09PM +1100, Peter Jeremy wrote:
> On 2008-Oct-15 02:08:48 -0700, Jeremy Chadwick <koitsu at FreeBSD.org> wrote:
> >On Wed, Oct 15, 2008 at 07:58:43PM +1100, Peter Jeremy wrote:
> >> On 2008-Oct-15 01:35:38 -0700, Jeremy Chadwick <koitsu at FreeBSD.org> wrote:
> >> >On Wed, Oct 15, 2008 at 07:24:28PM +1100, Peter Jeremy wrote:
> >> >> Last night, I attempted a full, compressed backup of my 181GB /home
> >> >> (on a PATA disk) to a remote system.  The backup started at 2159 and
> >> >> everything appeared normal until about 0040 when the system became
> >> >> non-responsive and this lasted until the dump completed at 1033.  This
> >> >> is the first full backup of /home I've made for several years (due to
> >> >> lack of space).
> >> ...
> >> >It's a known problem documented in my Wiki -- see "dump/restore".  Note
> >> >the part about UFS2 snapshot generation.  I'm almost certain this is
> >> >what you're describing.
> >> 
> >> * UFS2 snapshot generation (mksnap_ffs, dump -L) takes too long; system is unusable during this time
> >>   In my case, snapshot creation took ~4 minutes.  The system was
> >>   running normally for 2.6 hours after snapshot creation completed
> >>   before it froze.
> >
> >Did you read the References, including the one from myself?
> 
> Yes.  In my case, dump started and ran mksnap_ffs.  About 4 minutes
> later, actual dumping started and data streaming continued for about
> 12.6 hours.  The system froze about 2.6 hours into the dump (after
> dump had written about 31GB).
> 
> >Snapshot generation in some cases took only minutes, but *removal* of
> >the generated the snapshot took 1.5 hours or more, hanging the system
> >until the removal was complete.
> 
> Based on progress reports from both dump and my fifo process, the
> snapshot removal began about 10 hours _after_ the system froze
> (during this time, dump wrote about 143GB).  Given the timeline,
> it's fairly clear that neither mksnap_ffs nor the 'rm snapshot'
> were running at the time the system froze.  I am therefore quite
> confident that the problem I saw is not related to either creation
> or removal of snapshots.
> 
> I have been using FreeBSD snapshots for many years and am quite
> familiar with their quirks.  I have never seen this particular
> problem before.  (And FWIW, I _am_ using Doug Ambrisko's patch to
> ffs_snapshot.c).

I don't doubt your seniority or technical skill set.  I was simply
offering information that appeared relevant.

Sorry for the noise and incorrect correlation.

-- 
| 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 |