corrupt label - wrong magic number or corrupt label - label checksum failed

Cause

After a power cycle, the machine comes up with error messages saying: corrupt label - label checksum failed or corrupt label - wrong magic number . format(1M) showed:

  0 unassigned    wm       0               0         (0/0/0)          0
  1 unassigned    wm       0               0         (0/0/0)          0
  2     backup    wm       0 - 5460        4.2G    (5460/0/0)   4154160
  3 unassigned    wm       0               0         (0/0/0)          0
  4 unassigned    wm       0               0         (0/0/0)          0
  5 unassigned    wm       0               0         (0/0/0)          0
  6 unassigned    wm       0 - 2730       2.1G       (0/0/0)          0
  7 unassigned 	  wm       2730-5460      2.1G       (0/0/0)          0

The disk label (VTOC) is kept on the block 0 of cylinder 0. The label will eventually get overwritten by database programs using raw partitions if the raw partition begins at cylinder 0. (Unix filesystems avoid this area of the partition.)

Action

The workaround is to go into format and get the backup label using the backup command. Relabel the disk using this backup label. You should then be able to access the disk.

Backup the data on this disk.

Go back to the disk and relabel it, starting the raw partition at cylinder 1 (This looses one cylinder, but prevents corrupting the VTOC).

Label again.

Restore the data from your backup.