Veritas Volume Manager 5.0 Troubleshooting Guide, HP-UX 11i v3, First Edition, May 2008

19Recovery from hardware failure
Failures on RAID-5 volumes
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.
If a volume without valid RAID-5 logs is started and the process is killed before
the volume is resynchronized, the result is an active volume with stale parity.
For an example of the output of the
vxprint -ht command, see the following
example for a stale RAID-5 volume:
V NAME RVG/VSET/COKSTATE STATE LENGTH READPOL PREFPLEX UTYPE
PL NAME VOLUME KSTATE STATE LENGTH LAYOUT NCOL/WID MODE
SD NAME PLEX DISK DISKOFFS LENGTH [COL/]OFF DEVICE MODE
SV NAME PLEX VOLNAME NVOLLAYR LENGTH [COL/]OFF AM/NM MODE
...
v r5vol - ENABLED NEEDSYNC 204800 RAID - raid5
pl r5vol-01 r5vol ENABLED ACTIVE 204800 RAID 3/16 RW
sd disk01-01 r5vol-01disk01 0 102400 0/0 c2t9d0 ENA
sd disk02-01 r5vol-01disk02 0 102400 1/0 c2t10d0 dS
sd disk03-01 r5vol-01disk03 0 102400 2/0 c2t11d0 ENA
...
This output lists the volume state as NEEDSYNC, indicating that the parity needs
to be resynchronized. The state could also have been SYNC, indicating that a
synchronization was attempted at start time and that a synchronization process
should be doing the synchronization. If no such process exists or if the volume is
in the NEEDSYNC state, a synchronization can be manually started by using the
resync keyword for the vxvol command. For example, to resynchronize the
RAID-5 volume in the figure “Invalid RAID-5 volume” on page 22, use the
following command:
# vxvol -g mydg resync r5vol
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 resynchronizes a region equal to the number of sectors specified by
the -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 progress of parity regeneration must be kept
across reboots. 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