question about dump performance on a snapshot

How long should it take to run 'dump' on a snapshot?

I have a 6-disk raid 5 with 15K RPM scsi disk, so quite
fast. It is 300GB in size, with 20% occupied. There
are ~6000 files on this filesystem, all postgresql.

I stopped postgresql, did a file system snapshot, and
restarted postgresql. I then commenced a dump on the
snap as below:

dump -0 -a -C 32 -f $dumpfile -u $snapfile

dumpfile and snapfile are both on the same filesystem.

for the last 35 minutes, the size of the dump file has
not gone up, and dump is taking 0% cpu:

# dump -0 -a -C 32 -f $backupfile -u $outfile
  DUMP: Date of this level 0 dump: Mon Mar 29 16:32:25 2004
  DUMP: Date of last level 0 dump: the epoch
  DUMP: Dumping /data/snapshot/snap.1 to /data/backup/dump.1
  DUMP: mapping (Pass I) [regular files]
  DUMP: Cache 32 MB, blocksize = 65536
  DUMP: mapping (Pass II) [directories]
  DUMP: estimated 59867851 tape blocks.
  DUMP: dumping (Pass III) [directories]
  DUMP: dumping (Pass IV) [regular files]
load: 0.00  cmd: dump 39347 [runnable] 1.20u 5.70s 0% 48616k

# ps -wwax |grep dump
39584  p1  L+     0:00.00 grep dump
39336  d0  I+     0:01.61 dump -0 -a -C 32 -f /data/backup/dump.1 -u
/data/snapshot/snap.1 (dump)
39347  d0  I+     0:06.90 dump: /data/snapshot/snap.1: pass 4: 0.94% done,
finished in 1:34 (dump)
39348  d0  I+     0:08.18 dump -0 -a -C 32 -f /data/backup/dump.1 -u
/data/snapshot/snap.1 (dump)
39349  d0  I+     0:08.18 dump -0 -a -C 32 -f /data/backup/dump.1 -u
/data/snapshot/snap.1 (dump)
39350  d0  I+     0:08.26 dump -0 -a -C 32 -f /data/backup/dump.1 -u
/data/snapshot/snap.1 (dump)

Although the dump always indicates it is 'runnable' when i
hit ^T, it doesn't run, and doesn't consume any cpu.
The machine is idle.

machine is running current cvsup from march 21 on a dual
xeon 2.8 with asr raid controller.

# tunefs -p /dev/da0s1e
tunefs: ACLs: (-a)                                         disabled
tunefs: MAC multilabel: (-l)                               disabled
tunefs: soft updates: (-n)                                 enabled
tunefs: maximum blocks per file in a cylinder group: (-e)  2048
tunefs: average file size: (-f)                            16384
tunefs: average number of files in a directory: (-s)       64
tunefs: minimum percentage of free space: (-m)             8%
tunefs: optimization preference: (-o)                      time
tunefs: volume label: (-L)