VERITAS Volume Manager 4.1 Troubleshooting Guide

Recovery from Hardware Failure
Failures on RAID-5 Volumes
Chapter 1 23
Recovering a RAID-5 Volume
The types of recovery that may typically be required for RAID-5 volumes are the following:
• “Parity Resynchronization” on page 23
• “Log Plex Recovery” on page 25
• “Stale Subdisk Recovery” on page 25
Parity resynchronization and stale subdisk recovery are typically performed when the RAID-5
volume is started, or shortly after the system boots. They can also be performed by running
the vxrecover command.
For more information on starting RAID-5 volumes, see “Starting RAID-5 Volumes” on
page 26.
If hot-relocation is enabled at the time of a disk failure, system administrator intervention is
not required unless no suitable disk space is available for relocation. Hot-relocation is
triggered by the failure and the system administrator is notified of the failure by electronic
mail.
Hot relocation automatically attempts to relocate the subdisks of a failing RAID-5 plex. After
any relocation takes place, the hot-relocation daemon (vxrelocd) also initiate a parity
resynchronization.
In the case of a failing RAID-5 log plex, relocation occurs only if the log plex is mirrored; the
vxrelocd daemon then initiates a mirror resynchronization to recreate the RAID-5 log plex.
If hot-relocation is disabled at the time of a failure, the system administrator may need to
initiate a resynchronization or recovery.
NOTE Following severe hardware failure of several disks or other related subsystems
underlying a RAID-5 plex, it may be impossible to recover the volume using the
methods described in this chapter. In this case, remove the volume, recreate it
on hardware that is functioning correctly, and restore the contents of the
volume from a backup.
Parity Resynchronization
In most cases, a RAID-5 array does not have stale parity. Stale parity only occurs after all
RAID-5 log plexes for the RAID-5 volume have failed, and then only if there is a system
failure. Even if a RAID-5 volume has stale parity, it is usually repaired as part of the volume
start process.