VERITAS Volume Manager 3.1 Administrator's Guide

Recovery
Miscellaneous RAID-5 Operations
Chapter 8380
have multiple valid RAID-5 logs associated with the array. However, this
is not always possible.
To start a RAID-5 volume with stale subdisks, you can use the -f option
with the vxvol start command. This causes all stale subdisks to be
marked as nonstale. Marking takes place before the start operation
evaluates the validity of the RAID-5 volume and what is needed to start
it. Also, you can mark individual subdisks as nonstale by using the
command vxmend fix unstale subdisk .
Recovery When Starting RAID-5 Volumes
Several operations can be necessary to fully restore 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 is done to
prevent 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).
The following steps are taken 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 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
kernel state and setting the volume state to SYNC. Any log plexes are
left DISABLED
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