ZFS: can't read MOS

[Rumen Telbizov]

Hello everyone,

I have a ZFS FreeBSD 8.2-STABLE (Aug 30, 2011) that I am having issues with
and might use some help.

In a nutshell, this machine has been running fine for about a year and a
half but after a recent power
outage (complete colo blackout) I can't boot of the ZFS pool any more.
Here's the error I get (attached screenshot as well):

ZFS: i/o error - all block copies unavailable
ZFS: can't read MOS
ZFS: unexpected object set type 0
ZFS: unexpected object set type 0

FreeBSD/x86 boot
Default: zroot:/boot/kernel/kernel
boot: ZFS: unexpected object set type 0

I've been searching the net high and low for an actual solution but all the
threads end up nowhere.
I hope I can get some clue here. Thanks in advance.

Here's the relevant hardware configuration of this box (serves as a backup
box).

   - SuperMicro 4U + another 4U totalling 48 x 2TB disks
   - Hardware raid LSI 9261-8i holding both shelves giving 1 mfid0 device
   to the OS
   - Hardware raid 60 -- 6 x 8 raid6 groups
   - ZFS with gptzfsboot installed on the "single" mfid0 device. Partition
   table is:

[root at mfsbsd /zroot/etc]# gpart show -l
=>          34  140554616765  mfid0  GPT  (65T)
            34           128      1  (null)  (64k)
           162      33554432      2  swap  (16G)
      33554594  140521062205      3  zroot  (65T)



   - boot device is: vfs.root.mountfrom="zfs:zroot" (as per loader.conf)
   - zpool status is:

[root at mfsbsd /zroot/etc]# zpool status
  pool: zroot
 state: ONLINE
 scan: scrub canceled on Mon Apr  9 09:48:14 2012
config:

NAME        STATE     READ WRITE CKSUM
zroot       ONLINE       0     0     0
 mfid0p3   ONLINE       0     0     0

errors: No known data errors



   - zpool get all:

[root at mfsbsd /zroot/etc]# zpool get all zroot
NAME   PROPERTY       VALUE       SOURCE
zroot  size           65T         -
zroot  capacity       36%         -
zroot  altroot        -           default
zroot  health         ONLINE      -
zroot  guid           3339338746696340707  default
zroot  version        28          default
*zroot  bootfs         zroot       local*
zroot  delegation     on          default
zroot  autoreplace    off         default
zroot  cachefile      -           default
zroot  failmode       wait        default
zroot  listsnapshots  on          local
zroot  autoexpand     off         default
zroot  dedupditto     0           default
zroot  dedupratio     1.00x       -
zroot  free           41.2T       -
zroot  allocated      23.8T       -
zroot  readonly       off         -


Here's what happened chronologically:

   - Savvis Toronto blacked out completely for 31 minutes
   - After power was restored this machine came up with the above error
   - I managed to PXE boot into mfsbsd successfully and managed to import
   the pool and access actual data/snapshots - no problem
   - Shortly after another reboot the hardware raid controller complained
   that it has lost
   it's configuration and now sees only half of the disks as foreign good
   and the
   rest as foreign bad. BIOS didn't see any boot device.
   - Spent some time on the phone with LSI and managed to restore the
   hardware RAID
   by basically removing any and all configuration, making disks
   unconfigured good
   and recreating the array in exactly the same way as I created it in the
   beginning BUT
   with the important exception that I did NOT initialize the array.
   - After this I was back to square one where I could see all the data
   without any loss
   (via mfsbsd) but cannot boot of the volume any more.
   - First thing I tried was to restore the boot loader without any luck:
      gpart bootcode -b /boot/pmbr -p /boot/gptzfsboot -i 1 mfid0p1
   - Then out of desperation, took zfsboot, zfsloader, gptzfsboot from
   9.0-RELEASE and replaced them in /boot,
   reinitialized again - no luck
   - Currently running zdb -ccv zroot to check for any corruptions - I am
   afraid this will take forever since I have *23.8T* used space. No errors
   yet
   - One thing I did notice is that zdb zroot returned the metaslab
   information line by line very slowly (10-15 seconds a line). I don't know
   if it's related.
   - Another thing I tried (saw that in a thread) without any difference
   whatsoever was:

# cd src/sys/boot/i386/zfsboot
# make clean; make cleandir
# make obj ; make depend ; make
# cd i386/loader
# make install
# cd /usr/src/sys/boot/i386/zfsboot
# make install
# sysctl kern.geom.debugflags=16
# dd if=/boot/zfsboot of=/dev/da0 count=1
# dd if=/boot/zfsboot of=/dev/da0 skip=1 seek=1024
# reboot


At this point I am contemplating how to evacuate all the data from there or
better yet put some USB flash to boot from.
I could provide further details/execute commands if needed. Any help would
be appreciated.

Thank you,
-- 
Rumen Telbizov
http://telbizov.com