Veritas Volume Manager 4.1 Troubleshooting Guide (HP-UX 11i v3, February 2007)

Failures on RAID-5 Volumes
16 VERITAS Volume Manager Troubleshooting Guide
When this occurs, the vxvol start command returns the following error message:
VxVM vxvol ERROR V-5-1-1236 Volume r5vol is not startable; RAID-5
plex does not map entire volume length.
At this point, the contents of the RAID-5 volume are unusable.
Another possible way that a RAID-5 volume can become unstartable is if the parity is stale
and a subdisk becomes detached or stale. This occurs because within the stripes that
contain the failed subdisk, the parity stripe unit is invalid (because the parity is stale) and
the stripe unit on the bad subdisk is also invalid. The figure, “Invalid RAID-5 Volume” on
page 16, illustrates a RAID-5 volume that has become invalid due to stale parity and a
failed subdisk.
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 9 for details).
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