Veritas Volume Manager 5.0 Troubleshooting Guide Guide (September 2006)

24 Recovery from hardware failure
Failures on RAID-5 volumes
Figure 1-3 Invalid RAID-5 volume
This example shows four stripes in the RAID-5 array. All parity is stale and subdisk
disk05-00 has failed. This makes stripes X and Y unusable because two failures have
occurred within those stripes.
This qualifies as two failures within a stripe and prevents the use of the volume. In this
case, the output display from the
vxvol start command is as follows:
VxVM vxvol ERROR V-5-1-1237 Volume r5vol is not startable; some
subdisks are unusable and the parity is stale.
This situation can be avoided by always using two or more RAID-5 log plexes in RAID-5
volumes. RAID-5 log plexes prevent the parity within the volume from becoming stale
which prevents this situation (see “System failures” on page 17 for details).
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The subdisk is considered stale even though the data is not out of date (because the volume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:
disk00-00 disk01-00 disk02-00
disk03-00 disk04-00 disk05-00
RAID-5 plex
W
X
Y
Z
W
X
Y
Z
Data
Data
Data
Data
Data
Data
Data
Data
Parity
Parity
Parity
Parity