I've been having this for a while off and on and it is getting quite
On my main server I managed to work around it by unmounting the
partition, but now I cannot...

the problem is dump freezing during a backup of a live file system. I
have told it to use a snapshot.
the parameters are
dump -0uan -C 32 -L -f - /usr

it is doing this via ssh to a file on another server. / and /tmp on
the same box work fine, but /usr freezes every time. since 'ssh' is
on /usr I cannot unmount the fs for dump.
the other print server does the dump just fine. identicle setup, but
3 LPT ports instead of just 1, and a slightly faster processor (P200
vs P133)

here is the screen display

Fri May 9 12:58:56 SAST 2008 /usr
DUMP: Date of this level 0 dump: Fri May 9 12:59:00 2008
DUMP: Date of last level 0 dump: the epoch
DUMP: Dumping snapshot of /dev/ad0s1e (/usr) to standard output
DUMP: mapping (Pass I) [regular files]
DUMP: Cache 32 MB, blocksize = 65536
DUMP: mapping (Pass II) [directories]
DUMP: estimated 1073743 tape blocks.
DUMP: dumping (Pass III) [directories]
DUMP: 2.94% done, finished in 2:45 at Fri May 9 15:49:16 2008

at that point it sat for more than an hour before I ctrl-C'd it and
started looking for solutions.
I had this a lot on my main server when dumping to tape (24gb DAT).
this was just on the /home partition, the largest and most important
one of course. I got around that by umounting the partition before
the dump.
since the tapes took too long to have /home down for all the time, I
started dumping across the net to another server (to disk). thus it
can now dump during the night and be finished by the time people come
to work.

but now, with /usr freezing up I cannot umount it. here is the output
from df
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/ad0s1a 126702 53028 63538 45% /
devfs 1 1 0 100% /dev
/dev/ad0s1e 1217358 1048328 71642 94% /usr
/dev/ad0s1d 63214 146 58012 0% /tmp

uname -a
FreeBSD iwr09.iwr.ru.ac.za 5.5-SECURITY FreeBSD 5.5-SECURITY #0: Tue
Feb 12 22:58:05 UTC 2008 r...@builder.daemonology.net:/usr/obj/
src/sys/GENERIC i386

yes I know 5.5 is near EOL. the other freezes were on 6.2 so it is
not unique to 5.5
I see mention of dump freezing when I Google, but no solutions.

this machine is a print server so is a very basic install, with a
small HDD and not much else so I cannot imagine anything interfering,
except maybe a print job. however, this freeze happened twcie in
exactly the same place.