How to Recover From a Boot Device Failure (Command Line)

If you have a root (/) mirror and your boot device fails, you'll need to set up an alternate boot device.

The high-level steps in this task are:

• Booting from the alternate root (/) submirror

• Determining the errored state database replicas and metadevices

• Repairing the problem disk

• Restoring metadevice state database and metadevices to their original state

Example -- Recovering From a Boot Device Failure

In the following example, the boot device containing two of the six state database replicas and the root (/), swap, and /usr submirrors fails.

Initially, when the boot device fails, you'll see a message similar to the following. This message may differ among various architectures.

Rebooting with command:
Boot device: /iommu/sbus/dma@f,81000/esp@f,80000/sd@3,0   File and args: kadb
kadb: kernel/unix
The selected SCSI device is not responding
Can't open boot device
...

When you see this message, note the device. Then, follow these steps:

1. Boot from another root (/) submirror.

   Since only two of the six state database replicas in this example are in error, you can still boot. If this were not the case, you would need to delete the stale state database replicas in single-user mode. This procedure is described in "How to Recover From Insufficient State Database Replicas (Command Line)".

   When you created the mirror for the root (/) file system, you should have recorded the alternate boot device as part of that procedure. In this example, disk2 is that alternate boot device.

   ok boot disk2 ... SunOS Release 5.5 Version Generic [UNIX(R) System V Release 4.0] Copyright (c) 1983-1995, Sun Microsystems, Inc. Hostname: demo ... demo console login: root Password: <root-password> Last login: Wed Dec 16 13:15:42 on console SunOS Release 5.1 Version Generic [UNIX(R) System V Release 4.0] ...

2. Use the metadb(1M) command to determine that two state database replicas have failed.

   # metadb flags first blk block count M p unknown unknown /dev/dsk/c0t3d0s3 M p unknown unknown /dev/dsk/c0t3d0s3 a m p luo 16 1034 /dev/dsk/c0t2d0s3 a p luo 1050 1034 /dev/dsk/c0t2d0s3 a p luo 16 1034 /dev/dsk/c0t1d0s3 a p luo 1050 1034 /dev/dsk/c0t1d0s3

   The system can no longer detect state database replicas on slice /dev/dsk/c0t3d0s3, which is part of the failed disk.

3. Use the metastat(1M) command to determine that half of the root (/), swap, and /usr mirrors have failed.

   # metastat d0: Mirror Submirror 0: d10 State: Needs maintenance Submirror 1: d20 State: Okay ... d10: Submirror of d0 State: Needs maintenance Invoke: "metareplace d0 /dev/dsk/c0t3d0s0 <new device>" Size: 47628 blocks Stripe 0: Device Start Block Dbase State Hot Spare /dev/dsk/c0t3d0s0 0 No Maintenance d20: Submirror of d0 State: Okay Size: 47628 blocks Stripe 0: Device Start Block Dbase State Hot Spare /dev/dsk/c0t2d0s0 0 No Okay d1: Mirror Submirror 0: d11 State: Needs maintenance Submirror 1: d21 State: Okay ... d11: Submirror of d1 State: Needs maintenance Invoke: "metareplace d1 /dev/dsk/c0t3d0s1 <new device>" Size: 69660 blocks Stripe 0: Device Start Block Dbase State Hot Spare /dev/dsk/c0t3d0s1 0 No Maintenance d21: Submirror of d1 State: Okay Size: 69660 blocks Stripe 0: Device Start Block Dbase State Hot Spare /dev/dsk/c0t2d0s1 0 No Okay d2: Mirror Submirror 0: d12 State: Needs maintenance Submirror 1: d22 State: Okay ... d2: Mirror Submirror 0: d12 State: Needs maintenance Submirror 1: d22 State: Okay ... d12: Submirror of d2 State: Needs maintenance Invoke: "metareplace d2 /dev/dsk/c0t3d0s6 <new device>" Size: 286740 blocks Stripe 0: Device Start Block Dbase State Hot Spare /dev/dsk/c0t3d0s6 0 No Maintenance d22: Submirror of d2 State: Okay Size: 286740 blocks Stripe 0: Device Start Block Dbase State Hot Spare /dev/dsk/c0t2d0s6 0 No Okay

   In this example, the metastat shows that following submirrors need maintenance:

   • Submirror d10, device c0t3d0s0

   • Submirror d11, device c0t3d0s1

   • Submirror d12, device c0t3d0s6

4. Halt the system, repair the disk, and use the format(1M) command or the fmthard(1M) command, to partition the disk as it was before the failure.

   # halt ... Halted ... ok boot ... # format /dev/rdsk/c0t3d0s0

5. Reboot.

   Note that you must reboot from the other half of the root (/) mirror. You should have recorded the alternate boot device when you created the mirror.

   # halt ... ok boot disk2

6. To delete the failed state database replicas and then add them back, use the metadb(1M) command.

   # metadb flags first blk block count M p unknown unknown /dev/dsk/c0t3d0s3 M p unknown unknown /dev/dsk/c0t3d0s3 a m p luo 16 1034 /dev/dsk/c0t2d0s3 a p luo 1050 1034 /dev/dsk/c0t2d0s3 a p luo 16 1034 /dev/dsk/c0t1d0s3 a p luo 1050 1034 /dev/dsk/c0t1d0s3 # metadb -d c0t3d0s3 # metadb -c 2 -a c0t3d0s3 # metadb flags first blk block count a m p luo 16 1034 /dev/dsk/c0t2d0s3 a p luo 1050 1034 /dev/dsk/c0t2d0s3 a p luo 16 1034 /dev/dsk/c0t1d0s3 a p luo 1050 1034 /dev/dsk/c0t1d0s3 a u 16 1034 /dev/dsk/c0t3d0s3 a u 1050 1034 /dev/dsk/c0t3d0s3

7. Use the metareplace(1M) command to re-enable the submirrors.

   # metareplace -e d0 c0t3d0s0 Device /dev/dsk/c0t3d0s0 is enabled # metareplace -e d1 c0t3d0s1 Device /dev/dsk/c0t3d0s1 is enabled # metareplace -e d2 c0t3d0s6 Device /dev/dsk/c0t3d0s6 is enabled

   After some time, the resyncs will complete. You can now return to booting from the original device.