VERITAS Volume Manager 3.5 Troubleshooting Guide (September 2004)

Recovery from Hardware Failure
Failures on RAID-5 Volumes
Chapter 1
18
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 KSTATE STATE 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 disk01-01r5vol-01disk01 0 102400 0/0 c2t9d0 ENA
sd disk02-01r5vol-01disk02 0 102400 1/0 c2t10d0 dS
sd disk03-01r5vol-01disk03 0 102400 2/0 c2t11d0 ENA
pl r5vol-02 r5vol ENABLED LOG 1440 CONCAT - RW
sd disk04-01r5vol-02disk04 0 1440 0 c2t12d0 ENA
pl r5vol-03 r5vol ENABLED LOG 1440 CONCAT - RW
sd disk05-01r5vol-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-11 has failed:
V NAME RVG KSTATE STATE 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 RAID-5 ENABLED ACTIVE 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 ENA
sd disk03-01 r5vol-01disk03 0 102400 2/0 c2t11d0 ENA
pl r5vol-02 r5vol DISABLEDBADLOG 1440 CONCAT - RW
sd disk04-01 r5vol-11disk04 0 1440 0 c2t12d0 ENA
pl r5vol-03 r5vol ENABLED LOG 1440 CONCAT - RW
sd disk05-01 r5vol-12disk05 0 1440 0 c2t14d0 ENA