I have an interesting issue with one single ZFS filesystem in a pool.
All the other filesystems are fine, and can be mounted, snapshoted,
destroyed, etc.  But this one filesystem, if I try to do any operation
on it (zfs mount, zfs snapshot, zfs destroy, zfs set <anything>), it
spins the system until all RAM is used up (wired), and then hangs the
box.  The zfs process sits in tx -> tx_sync_done_cv state until the
box locks up.  CTRL+T of the process only ever shows this:
    load: 0.46  cmd: zfs 3115 [tx->tx_sync_done_cv)] 36.63r 0.00u 0.00s 0% 2440k

Anyone come across anything similar?  And found a way to fix it, or to
destroy the filesystem?  Any suggestions on how to go about debugging
this?  Any magical zdb commands to use?

The filesystem only has 5 MB of data in it (log files), compressed via
LZJB for a compressratio of ~6x.  There are no snapshots for this

Dedupe is enabled on the pool and all filesystems.

System is running 64-bit FreeBSD 9.0:
FreeBSD alphadrive.sd73.bc.ca 9.0-RELEASE FreeBSD 9.0-RELEASE #0
r229803: Sun Jan  8 00:43:00 PST 2012
r...@alphadrive.sd73.bc.ca:/usr/obj/usr/src/sys/ZFSHOST90  amd64

Hardware is fairly generic:
  - SuperMicro H8DGi-F motherboard
  - AMD Opteron 6128 CPU (8 cores)
  - 24 GB of DDR3 RAM
  - 3x SuperMicro AOC-USAS-L8i SATA controllers
  - 24x harddrives ranging from 500 GB to 2.0 TB (6 of each kind in
raidz2 vdevs)
  - 64 GB SSD partitioned for OS, swap, with 32 GB for L2ARC

Filesystem properties:
# zfs get all storage/logs/rsync
NAME                PROPERTY              VALUE                  SOURCE
storage/logs/rsync  type                  filesystem             -
storage/logs/rsync  creation              Tue May 10  9:55 2011  -
storage/logs/rsync  used                  5.48M                  -
storage/logs/rsync  available             4.61T                  -
storage/logs/rsync  referenced            5.48M                  -
storage/logs/rsync  compressratio         5.93x                  -
storage/logs/rsync  mounted               no                     -
storage/logs/rsync  quota                 none                   default
storage/logs/rsync  reservation           none                   default
storage/logs/rsync  recordsize            128K                   default
storage/logs/rsync  mountpoint            /var/log/rsync         local
storage/logs/rsync  sharenfs              off                    default
storage/logs/rsync  checksum              sha256
inherited from storage
storage/logs/rsync  compression           lzjb
inherited from storage
storage/logs/rsync  atime                 off
inherited from storage
storage/logs/rsync  devices               on                     default
storage/logs/rsync  exec                  on                     default
storage/logs/rsync  setuid                on                     default
storage/logs/rsync  readonly              off                    default
storage/logs/rsync  jailed                off                    default
storage/logs/rsync  snapdir               visible
inherited from storage
storage/logs/rsync  aclmode               discard                default
storage/logs/rsync  aclinherit            restricted             default
storage/logs/rsync  canmount              on                     default
storage/logs/rsync  xattr                 on                     default
storage/logs/rsync  copies                1                      default
storage/logs/rsync  version               5                      -
storage/logs/rsync  utf8only              off                    -
storage/logs/rsync  normalization         none                   -
storage/logs/rsync  casesensitivity       sensitive              -
storage/logs/rsync  vscan                 off                    default
storage/logs/rsync  nbmand                off                    default
storage/logs/rsync  sharesmb              off                    default
storage/logs/rsync  refquota              none                   default
storage/logs/rsync  refreservation        none                   default
storage/logs/rsync  primarycache          all
inherited from storage
storage/logs/rsync  secondarycache        metadata
inherited from storage
storage/logs/rsync  usedbysnapshots       0                      -
storage/logs/rsync  usedbydataset         5.48M                  -
storage/logs/rsync  usedbychildren        0                      -
storage/logs/rsync  usedbyrefreservation  0                      -
storage/logs/rsync  logbias               latency                default
storage/logs/rsync  dedup                 sha256
inherited from storage
storage/logs/rsync  mlslabel                                     -
storage/logs/rsync  sync                  standard               default
storage/logs/rsync  refcompressratio      5.93x

Freddie Cash
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