Veritas Volume Manager 5.0 Troubleshooting Guide Guide (September 2006)

18 Recovery from hardware failure

Failures on RAID-5 volumes

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: