VERITAS Volume Manager 3.5 Troubleshooting Guide (September 2004)

Recovery from Hardware Failure
Failures on RAID-5 Volumes
Chapter 1
22
• the RAID-5 volume is stopped but was not shut down cleanly; that is, the parity is
considered stale
• the RAID-5 volume is active and has no valid log areas
Only the third case can be overridden by using the -o force option.
Subdisks of RAID-5 volumes can also be split and joined by using the vxsd split
command and the vxsd join command. These operations work the same way as those
for mirrored volumes.
NOTE RAID-5 subdisk moves are performed in the same way as subdisk moves for other
volume types, but without the penalty of degraded redundancy.
Starting RAID-5 Volumes
When a RAID-5 volume is started, it can be in one of many states. After a normal system
shutdown, the volume should be clean and require no recovery. However, if the volume
was not closed, or was not unmounted before a crash, it can require recovery when it is
started, before it can be made available. This section describes actions that can be taken
under certain conditions.
Under normal conditions, volumes are started automatically after a reboot and any
recovery takes place automatically or is done through the vxrecover command.
Unstartable RAID-5 Volumes
A RAID-5 volume is unusable if some part of the RAID-5 plex does not map the volume
length:
• the RAID-5 plex cannot be sparse in relation to the RAID-5 volume length
• the RAID-5 plex does not map a region where two subdisks have failed within a
stripe, either because they are stale or because they are built on a failed disk
When this occurs, the vxvol start command returns the following error message:
vxvm:vxvol: ERROR: 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 situation shown in
Figure 1-3, “Invalid RAID-5 Volume,” illustrates a RAID-5 volume that has become
invalid due to stale parity and a failed subdisk.