System Administration Guide: Basic Administration

Recovering a Corrupted Disk Label

Sometimes, a power or system failure causes a disk's label to become unrecognizable. A corrupted disk label doesn't always mean that the slice information or the disk's data must be recreated or restored.

The first step to recovering a corrupted disk label is to label the disk with the correct geometry and disk type information. You can complete this step through the normal disk labeling method, by using either automatic configuration or manual disk type specification.

If the format utility recognizes the disk type, the next step is to search for a backup label to label the disk. Labeling the disk with the backup label labels the disk with the correct partitioning information, the disk type, and disk geometry.

How to Recover a Corrupted Disk Label

Boot the system to single-user mode.

If necessary, boot the system from a local CD-ROM or the network in single-user mode to access the disk.

See Chapter 13, SPARC: Booting a System (Tasks) or Chapter 14, IA: Booting a System (Tasks) for information on booting the system.

Relabel the disk.
# format
At this point, the format utility attempts to automatically configure any unlabeled SCSI disk. If the format utility is able to configure the unlabeled and corrupted disk, it will display:
cwtxdy: configured with capacity of abcMB
The format utility then displays the list of disks on the system.

Type the number of the disk that you need to recover from the list displayed on your screen.
Specify disk (enter its number): 1

Select one of the following to determine how to label the disk.
1. If the disk was configured successfully, follow steps 5 and 6. Then go to step 12.
2. If the disk was not configured successfully, follow steps 7-11. Then go to step 12.

Search for the backup label.

format> verify
Warning: Could not read primary label.
Warning: Check the current partitioning and 'label' the disk or 
use the 'backup' command.
Backup label contents:
Volume name = <        >
ascii name  = <SUN1.05 cyl 2036 alt 2 hd 14 sec 72>
pcyl        = 2038
ncyl        = 2036
acyl        =    2
nhead       =   14
nsect       =   72
Part      Tag    Flag     Cylinders        Size            Blocks
  0       root    wm       0 -  300      148.15MB    (301/0/0)   303408
  1       swap    wu     301 -  524      110.25MB    (224/0/0)   225792
  2     backup    wm       0 - 2035     1002.09MB    (2036/0/0) 2052288
  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        usr    wm     525 - 2035      743.70MB    (1511/0/0) 1523088
  7 unassigned    wm       0               0         (0/0/0)          0

If the format utility was able to find a backup label and the backup label contents appear satisfactory, use the backup command to label the disk with the backup label.
format> backup Disk has a primary label, still continue? y Searching for backup labels...found. Restoring primary label
The disk label has been recovered. Go to step 12.

If the format utility was not able to automatically configure the disk, specify the disk type by using the type command.
format> type
The Available Drives Type menu is displayed.

Select 0 to automatically configure the disk, or select a disk type from the list of possible disk types.
Specify disk type (enter its number)[12]: 12

If the disk was successfully configured, reply with no when the format utility asks if you want to label the disk.
Disk not labeled. Label it now? no

Use the verify command to search for backup labels.

format> verify
Warning: Could not read primary label.
Warning: Check the current partitioning and 'label' the disk
or use the 'backup' command.
.
.
.

If the format utility was able to find a backup label and the backup label contents appear satisfactory, use the backup command to label the disk with the backup label.
format> backup Disk has a primary label, still continue? y Searching for backup labels...found. Restoring primary label
The disk label has been recovered.

Exit the format utility.
format> q

Verify the file systems on the recovered disk by using the fsck command.

For information on using the fsck command, see Chapter 42, Checking UFS File System Consistency (Tasks).