Veritas Volume Manager 4.1 Troubleshooting Guide (HP-UX 11i v3, February 2007)

Failures on RAID-5 Volumes
10 VERITAS Volume Manager Troubleshooting Guide
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/COKSTATESTATE LENGTH READPOL PREFPLEX UTYPE
PL NAME VOLUME KSTATE STATE LENGTH LAYOUT NCOL/WID MODE
SD NAME PLEX DISK DISKOFFSLENGTH [COL/]OFF DEVICE MODE
SV NAME PLEX VOLNAME NVOLLAYRLENGTH [COL/]OFF AM/NM MODE
...
v r5vol - ENABLED DEGRADED204800 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.