[nycbug-talk] drives swapped around - bad superblock

[Judd Maltin]

Hi Folks,

I come, hat in hand, trying to fix a messed up FreeBSD system. I cut my
Unix teeth on FreeBSD 2.2.5.  I see a few things have changed since
then.  Now more /dev/wd0.   :)

I'm running:

FreeBSD 6.1-RELEASE-p16 FreeBSD 6.1-RELEASE-p16 #0: Mon Apr 30 10:44:59
PDT 2007

My disks started to die, or get messed up or something, so my hosting
facility put in a new drive, put their typical root partition image on
it, and now I have this:

# mount
/dev/ad7s1a on / (ufs, local)
devfs on /dev (devfs, local)
/dev/ad4s1a on /mnt/ad4s1a (ufs, local, soft-updates)
/dev/ad6s1c on /mnt/ad6s1c (ufs, local, soft-updates)

That's all fine and dandy, but dmesg shows me I have more goodies:

...snip..
ad4: 476940MB <Seagate ST3500630AS 3.AAC> at ata2-master SATA150
ad5: 715404MB <Seagate ST3750640AS 3.AAD> at ata2-slave SATA150
ad6: 715404MB <Seagate ST3750640AS 3.AAD> at ata3-master SATA150
ad7: 476940MB <Seagate ST3500630AS 3.AAK> at ata3-slave SATA150

And so I checked up on them with bsdlabel:
# bsdlabel ad4
bsdlabel: /dev/ad4: no valid label found
# bsdlabel ad4s1
# /dev/ad4s1:
8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  a: 155877293  4194304    4.2BSD        0     0     0
  b:  4194304        0      swap
  c: 160071597        0    unused        0     0         # "raw" part,
don't edit

# bsdlabel ad5s1
# /dev/ad5s1:
8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  c: 1465144002        0    unused     2048 16384         # "raw" part,
don't edit

# bsdlabel ad6s1
# /dev/ad6s1:
8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  c: 1465144002        0    unused     2048 16384         # "raw" part,
don't edit

# bsdlabel ad7s1
# /dev/ad7s1:
8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  a: 972565697        0    4.2BSD     2048 16384 28512
  b:  4194304 972565697      swap
  c: 976760001        0    unused        0     0         # "raw" part,
don't edit

I find it very interesting that I can mount /dev/ad6s1c just fine, that
/dev/ad5s1c also mounts just fine.. but not when I reboot.  I get bad
superblocks.

So, I've been a Linux guy for some time, so I try to fsck -t 4.2bsd
/dev/ad5s1 (guessing at the type from the above):

# fsck -t 4.2bsd /dev/ad5s1c
** /dev/ad5s1c
BAD SUPER BLOCK: VALUES IN SUPER BLOCK DISAGREE WITH THOSE IN FIRST
ALTERNATE
/dev/ad5s1c: NOT LABELED AS A BSD FILE SYSTEM (unused)

That partition holds all of our backups for the past 6 months.  I can't
lose it.  Oh, and it's in California.

Uh-oh.  This is where I stop.  I need a FreeBSD superhero at this point.
 I need to perform a little surgery here on this disk, slice and
partition, and I don't want to mess up.

Help?