VERITAS Volume Manager 4.1 Troubleshooting Guide

Recovery from Hardware Failure
Failures on RAID-5 Volumes
Chapter 1 27
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: 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 19 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The subdisk is considered stale even though the data is not out of date (because the volume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