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.

Under normal conditions, volumes are started automatically after a reboot and any recovery takes place automatically or is done through the vxrecover command.

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.

Figure: Invalid RAID-5 volume illustrates a RAID-5 volume that has become invalid due to stale parity and a failed subdisk.

There are 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.