Veritas Volume Manager 5.0.1 Troubleshooting Guide, HP-UX 11i v3, First Edition, November 2009

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:
■ 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 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.
Warning: The -o unsafe start option is considered dangerous, as it can make
the contents of the volume unusable. Using it is not recommended.
■ Any existing log plexes are zeroed and enabled. If all logs fail during this
process, the start process is aborted.
■ 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.
Recovery of RAID-5 volumes
The following types of recovery may be required for RAID-5 volumes:
■ Resynchronization of parity
■ Reattachment of a failed RAID-5 log plex
■ Recovery of a stale subdisk
21Recovering from hardware failure
Failures on RAID-5 volumes