dump freezes system

Question

dump -h 0 -0Lauf /backup/ada0p2.dump / - causes total system freeze.

server# cat /etc/fstab
# Device        Mountpoint      FStype  Options Dump    Pass#
/dev/ada0p2     /               ufs     rw      1       1
/dev/ada0p3     none            swap    sw      0       0
/dev/ada1p1     /backup         ufs     rw      2       2

nodump flags are set to /backup and /usr/home

following options are set to make sure there are no errors on the disks.

fsck_y_enable="YES"
background_fsck="NO"

FreeBSD 9.0-RELEASE amd64

Please help.

EDIT: This is the last stats I can get before system freezes

server# top
...
42 processes:  2 running, 40 sleeping
CPU:  0.0% user,  0.0% nice, 47.6% system,  3.6% interrupt, 48.8% idle
Mem: 71M Active, 39M Inact, 139M Wired, 420K Cache, 124M Buf, 1718M Free
Swap: 4096M Total, 4096M Free

  PID USERNAME    THR PRI NICE   SIZE    RES STATE   C   TIME   WCPU COMMAND
 1723 root          1  97    0 10056K  1188K CPU0    0   0:18 85.06% mksnap_ffs
 1711 root          1  20    0 10056K  1360K wait    1   0:00  0.00% dump

Answer 1

There's at least one known problem with mksnap_ffs in 9.0 on UFS filesystems; see this bug fix notice. Unless you want to run the bleeding edge stuff, I think you should dump without -L until 9.1.