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The subdisk is considered stale even though the data is not out of date (because the volume was in use when the subdisk was unavailable) and the RAID-5 volume is considered invalid.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 volume whenever possible.
To forcibly start a RAID-5 volume with stale subdisks
# vxvol [-g diskgroup] -f start r5vol
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. You can mark individual subdisks as non-stale by using the following command:
# vxmend [-g diskgroup] fix unstale subdisk
If some subdisks are stale and need recovery, and if valid logs exist, the volume is enabled by placing it in the ENABLED kernel state and the volume is available for use during the subdisk recovery. Otherwise, the volume kernel state is set to DETACHED and it is not available during subdisk recovery. This is done because if the system were to crash or if the volume were ungracefully stopped while it was active, the parity becomes stale, making the volume unusable. If this is undesirable, the volume can be started with the -o unsafe start option.
Warning: |
The -o unsafe start option is considered dangerous, as it can make the contents of the volume unusable. It is therefore not recommended. |
The volume state is set to RECOVER, and stale subdisks are restored. As the data on each subdisk becomes valid, the subdisk is marked as no longer stale. If the recovery of any subdisk fails, and if there are no valid logs, the volume start is aborted because the subdisk remains stale and a system crash makes the RAID-5 volume unusable. This can also be overridden by using the -o unsafe start option.
If the volume has valid logs, subdisk recovery failures are noted but they do not stop the start procedure.
When all subdisks have been recovered, the volume is placed in the ENABLED kernel state and marked as ACTIVE.