VERITAS Volume Manager 4.1 Troubleshooting Guide

Recovery from Hardware Failure
Failures on RAID-5 Volumes
Chapter 122
sd disk04-01 r5vol-02 disk04 0 1440 0 c2t12d0 ENA
pl r5vol-03 r5vol ENABLED LOG 1440 CONCAT - RW
sd disk05-01 r5vol-12 disk05 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:
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.