Veritas Volume Manager 5.0 Troubleshooting Guide Guide (September 2006)

19Recovery from hardware failure
Failures on RAID-5 volumes
sd disk03-01 r5vol-01disk03 0 102400 2/0 c2t11d0 ENA
pl r5vol-02 r5vol DISABLED BADLOG 1440 CONCAT - RW
sd disk04-01 r5vol-02disk04 0 1440 0 c2t12d0 ENA
pl r5vol-03 r5vol ENABLED LOG 1440 CONCAT - RW
sd disk05-01 r5vol-12disk05 0 1440 0 c2t14d0 ENA
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:
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, go 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.
2 Any existing log plexes are zeroed and enabled. If all logs fail during this process, the
start process is aborted.
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: