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).
>
> I noticed the non-responsiveness at about 0500 when:
> - The dump, gzip and fifo pipeline were running normally.
> - A 'systat -v' I had started was running normally (though it
> reported an excessive number of 'D' processes). Other values
> all appeared normal.
> - No response to return key at a zsh prompt
> - No response to up/down arrows in mutt
> [above all done in pre-existing ssh sessions from another host]
> - telnet to port 22 connected but didn't produce a banner.
>
> The duration above is based on system logs - which show nothing
> happened during this period. At the end, there were various anomolous
> entries:
> Oct 15 10:33:27 server ntpd[750]: too many recvbufs allocated (40)
> Oct 15 10:33:30 server sshd[947]: error: accept: Software caused connection
abort
> Oct 15 10:33:34 server kernel: TCP: [192.168.123.123]:59516 to
[192.168.123.200]:25 tcpflags 0x4<RST>; syncache_chkrst: Spurious RST
without matching syncache entry (possibly syncookie only), segment ignored
>
> Possibly useful information:
> The dump pipeline was:
> dump -uaL0 -C 32 -f - /home | reblock | gzip [stdout connected to socket
> to remote server]
> 'reblock' is basically a 200MB FIFO I wrote to desynchronise the
(often
> I/O bound) dump from the CPU-bound gzip.
>
> server% uname -a
> FreeBSD server.vk2pj.dyndns.org 7.0-STABLE FreeBSD 7.0-STABLE #18: Sun May
18 15:02:39 EST 2008
root@server.vk2pj.dyndns.org:/var/obj/k7/usr/src/sys/server i386
> server% df -ki
> Filesystem 1024-blocks Used Avail Capacity iused ifree %iused
Mounted on
> /dev/ad0s3d 204648864 181911710 6365246 97% 1703016 11353942 13%
/home
>
> About the only think that happened at around this time was nightly
> updates. These start at 0005, fetching CTM cvs-cur updates, applying
> them to /home/ncvs, then cvs updating /home/ports. Looking at
> timestamps, /home/ports/graphics/icod/CVS/Entries was updated at
> 0042 and /home/ports/graphics/imlib2_loaders/CVS/Entries (the next
> entry) was updated at 1034.
>
> Whilst /home is fairly full, I can't see that the snapshot meta and
> rollback data would have occupied the 20GB free (and no
'out-of-space'
> messages were generated). Is there some limit on the number of inodes
> that can be updated whilst a snapshot exists?
>
> Has anyone else seen anything similar?
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.
http://wiki.freebsd.org/JeremyChadwick/Commonly_reported_issues
This is one of the many reasons why I moved our backup infrastructure
over to use rsnapshot/rsync, despite the atime modification problem.
--
| 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 |