VERITAS Volume Manager 3.5 Troubleshooting Guide (August 2002)

Chapter 1, Recovery from Hardware Failure
Failures on RAID-5 Volumes
11
Parity is regenerated by issuing VOL_R5_RESYNC ioctls to the RAID-5 volume. The
resynchronization process starts at the beginning of the RAID-5 volume and
resynchronizesa region equal tothe number of sectorsspecified bythe -o iosize option. If
the -o iosize option is not specified, the default maximum I/O size is used. The resync
operation then moves onto the next region until the entire length of the RAID-5 volume
has been resynchronized.
For larger volumes, parity regeneration can take a long time. It is possible that the system
could be shut down or crash before the operation is completed. In case of a system
shutdown, the progressof parityregenerationmust bekept acrossreboots.Otherwise, the
process has to start all over again.
To avoid the restart process, parity regeneration is checkpointed.This means that the offset
up to which the parity has been regenerated is saved in the configuration database. The
-o checkpt=size option controls how often the checkpoint is saved. If the option is not
specified, the default checkpoint size is used.
Because saving the checkpoint offset requires a transaction, making the checkpoint size
too small can extend the time required to regenerate parity. After a system reboot, a
RAID-5 volumethat has a checkpointoffset smallerthan the volume length starts a parity
resynchronization at the checkpoint offset.
Log Plex Recovery
RAID-5 log plexes can become detached due to disk failures. These RAID-5 logs can be
reattached by using the att keyword for the vxplex command. To reattach the failed
RAID-5 log plex, use the following command:
# vxplex att r5vol r5vol-l1
Stale Subdisk Recovery
Stale subdisk recovery is usually done at volume start time. However, the process doing
the recovery can crash, or the volume may be started with an option such as -o
delayrecover that prevents subdisk recovery. In addition, the disk on which the
subdisk resides can be replaced without recovery operations being performed. In such
cases, you can perform subdisk recovery using the vxvol recover command. For
example, to recover the stale subdisk in the RAID-5 volume shown in the figure “Invalid
RAID-5 Volume” on page 13, use the following command:
# vxvol recover r5vol disk01-00
A RAID-5 volume that has multiple stale subdisks can be recovered in one operation. To
recover multiple stale subdisks, use the vxvol recover command on the volume, as
follows:
# vxvol recover r5vol