VERITAS Volume Manager 3.5 Troubleshooting Guide (September 2004)

Recovery from Hardware Failure

Failures on RAID-5 Volumes

Chapter 1

Default Startup Recovery Process for RAID-5

VxVM may need to perform several operations to restore fully the contents of a RAID-5

volume and make it usable. Whenever a volume is started, any RAID-5 log plexes are

zeroed before the volume is started. This prevents random data from being interpreted

as a log entry and corrupting the volume contents. Also, some subdisks may need to be

recovered, or the parity may need to be resynchronized (if RAID-5 logs have failed).

VxVM takes the following steps when a RAID-5 volume is started:

Step 1. If the RAID-5 volume was not cleanly shut down, it is checked for valid RAID-5 log

plexes.

• If valid log plexes exist, they are replayed. This is done by placing the volume in the

DETACHED volume kernel state and setting the volume state to REPLAY, and enabling

the RAID-5 log plexes. If the logs can be successfully read and the replay is

successful, move on to Step 2.

• If no valid logs exist, the parity must be resynchronized. Resynchronization is done

by placing the volume in the DETACHED volume kernel state and setting the volume

state to SYNC. Any log plexes are left in the DISABLED plex kernel state.

The volume is not made available while the parity is resynchronized because any

subdisk failures during this period makes the volume unusable. This can be

overridden by using the -o unsafe start option with the vxvol command. If any

stale subdisks exist, the RAID-5 volume is unusable.

CAUTION The -o unsafe start option is considered dangerous, as it can make the contents of

the volume unusable. Using it is not recommended.

Step 2. Any existing log plexes are zeroed and enabled. If all logs fail during this process, the

start process is aborted.

Step 3. If no stale subdisks exist or those that exist are recoverable, the volume is put in the

ENABLED volume kernel state and the volume state is set to ACTIVE. The volume is now

started.

Recovering a RAID-5 Volume

The types of recovery that may typically be required for RAID-5 volumes are the

following:

• “Parity Resynchronization” on page 20

• “Log Plex Recovery” on page 21

• “Stale Subdisk Recovery” on page 21

Parity resynchronization and stale subdisk recovery are typically performed when the

RAID-5 volume is started, or shortly after the system boots. They can also be performed

by running the vxrecover command.

For more information on starting RAID-5 volumes, see “Starting RAID-5 Volumes” on

page 22.