Veritas Volume Manager 5.0 Troubleshooting Guide, HP-UX 11i v3, First Edition, May 2008

23Recovery from hardware failure
Failures on RAID-5 volumes
Forcibly starting RAID-5 volumes
You can start a volume even if subdisks are marked as stale: for example, if a
stopped volume has stale parity and no RAID-5 logs, and a disk becomes
detached and then reattached.
The subdisk is considered stale even though the data is not out of date (because
the volume was in use when the subdisk was unavailable) and the RAID-5
volume is considered invalid. To prevent this case, always have multiple valid
RAID-5 logs associated with the array whenever 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 non-stale.
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 non-stale by using the following command:
# vxmend [-g diskgroup ] fix unstale subdisk
■ If some subdisks are stale and need recovery, and if valid logs exist, the
volume is enabled by placing it in the ENABLED kernel state and the volume
is available for use during the subdisk recovery. Otherwise, the volume
kernel state is set to DETACHED and it is not available during subdisk
recovery.
This is done because if the system were to crash or the volume was
ungracefully stopped while it was active, the parity becomes stale, making
the volume unusable. If this is undesirable, the volume can be started with
the -o unsafe start option.
Caution: The -o unsafe start option is considered dangerous, as it can
make the contents of the volume unusable. It is therefore not
recommended.
■ The volume state is set to RECOVER and stale subdisks are restored. As the
data on each subdisk becomes valid, the subdisk is marked as no longer
stale.
If any subdisk recovery fails and there are no valid logs, the volume start is
aborted because the subdisk remains stale and a system crash makes the
RAID-5 volume unusable. This can also be overridden by using the -o
unsafe start option.
Caution: The -o unsafe start option is considered dangerous, as it can
make the contents of the volume unusable. It is therefore not
recommended.
If the volume has valid logs, subdisk recovery failures are noted but they do
not stop the start procedure.