snapshot dump hangs
rwatson at freebsd.org
Wed Jun 9 04:08:00 GMT 2004
On Tue, 8 Jun 2004, Randy Bush wrote:
> i try to dump a live filesys with
> /sbin/rdump 0Luaf remote.sys:/backup/foo/var.dump /dev/twed0s1d
> the screen does
> DUMP: Connection to remote.sys established.
> DUMP: Date of this level 0 dump: Wed Jun 9 01:52:32 2004
> DUMP: Date of last level 0 dump: the epoch
> DUMP: Dumping snapshot of /dev/twed0s1d (/var) to /backup/foo/var.dump on host remote.sys
> DUMP: mapping (Pass I) [regular files]
> DUMP: mapping (Pass II) [directories]
> DUMP: estimated 513616 tape blocks.
> DUMP: dumping (Pass III) [directories]
> DUMP: dumping (Pass IV) [regular files]
> and then just hangs forever
> there is nothing in /var/.snap
dump unlinks the snapshot as soon as it opens it so that it will be GC'd
when dump is done...
> i can
> mount -u -o snapshot /var/.snap/snap1 /var
And this doesn't hang, or does?
> this is horrifyingly reproducable and happens with other source
I'm using dump with -L regularly with a recent -CURRENT box at work for
backups. On the whole, it's worked without problems, but I did once
observe dump hanging, in the sbwait state (suggesting it's blocked on
socket I/O?). At the time, I was unable to do much diagnosis. Could you
do a couple of things:
(1) Could you do a "ps awxl" and see what wait channel dump is blocked on?
(2) Could you break into DDB and generate a stack trace for dump?
(3) Could you run "show lockedvnods" in DDB and show the results?
(4) Could you run "show locks <pid>" on the dump process?
Robert N M Watson FreeBSD Core Team, TrustedBSD Projects
robert at fledge.watson.org Senior Research Scientist, McAfee Research
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