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

16 Recovery from hardware failure
Failures on RAID-5 volumes
Disk failures
An uncorrectable I/O error occurs when disk failure, cabling or other problems
cause the data on a disk to become unavailable. For a RAID-5 volume, this means
that a subdisk becomes unavailable. The subdisk cannot be used to hold data and
is considered stale and detached. If the underlying disk becomes available or is
replaced, the subdisk is still considered stale and is not used.
If an attempt is made to read data contained on a stale subdisk, the data is
reconstructed from data on all other stripe units in the stripe. This operation is
called a reconstructing-read. This is a more expensive operation than simply
reading the data and can result in degraded read performance. When a RAID-5
volume has stale subdisks, it is considered to be in degraded mode.
A RAID-5 volume in degraded mode can be recognized from the output of the
vxprint -ht command as shown in the following display:
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 DEGRADED 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
pl r5vol-02 r5vol ENABLED LOG 1440 CONCAT - RW
sd disk04-01 r5vol-02disk04 0 1440 0 c2t12d0 ENA
pl r5vol-03 r5vol ENABLED LOG 1440 CONCAT - RW
sd disk05-01 r5vol-03disk05 0 1440 0 c2t14d0 ENA
The volume r5vol is in degraded mode, as shown by the volume state, which is
listed as DEGRADED. The failed subdisk is disk02-01, as shown by the MODE
flags; d indicates that the subdisk is detached, and S indicates that the subdisk’s
contents are stale.
Note: Do not run the vxr5check command on a RAID-5 volume that is in
degraded mode.
A disk containing a RAID-5 log plex can also fail. The failure of a single RAID-5
log plex has no direct effect on the operation of a volume provided that the
RAID-5 log is mirrored. However, loss of all RAID-5 log plexes in a volume makes
it vulnerable to a complete failure. In the output of the
vxprint -ht command,
failure within a RAID-5 log plex is indicated by the plex state being shown as
BADLOG rather than LOG. This is shown in the following display, where the
RAID-5 log plex r5vol-02 has failed: