VxVM Veritas disk group configuration records

Veritas disk group configuration records

Veritas uses disk group configuration records to store subdisk, plex, volume, and device configuration data. The configuration records get written to the private region of specific devices in each disk group, and are described in the vxinfo(1m) manual page:

A disk group configuration is a small database
that contains all volume, plex, subdisk, and disk
media records. These configurations are repli-
cated onto some or all disks in the disk group,
usually with one copy on each disk. Because these
databases are stored within disk groups, record
associations cannot span disk groups. Thus, a
subdisk defined on a disk in one disk group cannot
be associated with a volume in another disk group.

If multiple devices are present in a disk group, Veritas will replicate the configuration records to multiple devices for redundancy. You can see which devices contain disk configuration records by invoking vxdg(1m) with the “list” option:

$ vxdg list oof

Group: oof
dgid: 1120604922.22.tigger
import-id: 1024.10
flags: cds
version: 120
alignment: 8192 (bytes)
ssb: on
detach-policy: global
dg-fail-policy: dgdisable
copies: nconfig=2 nlog=default
config: seqno=0.17098 permlen=1280 free=1223 templen=27 loglen=192
config disk c1t1d0s2 copy 1 len=1280 state=clean online
config disk c1t2d0s2 copy 1 len=1280 state=clean online
config disk c1t3d0s2 copy 1 len=1280 disabled
config disk c1t4d0s2 copy 1 len=1280 disabled
config disk c1t5d0s2 copy 1 len=1280 disabled
config disk c1t6d0s2 copy 1 len=1280 disabled
log disk c1t1d0s2 copy 1 len=192
log disk c1t2d0s2 copy 1 len=192
log disk c1t3d0s2 copy 1 len=192
log disk c1t4d0s2 copy 1 len=192
log disk c1t5d0s2 copy 1 len=192

This example shows that targets 1 and 2 contain configuration records. If you are a paranoid person, you will probably want to replicate the configuration records to several devices in the disk group. This can be accomplished with the vxedit(1m) utility:

$ vxedit -g oof set nconfig=6 oof

$ vxdg list oof | grep ^config

config: seqno=0.17137 permlen=1280 free=1265 templen=27 loglen=192
config disk c1t1d0s2 copy 1 len=1280 state=clean online
config disk c1t2d0s2 copy 1 len=1280 state=clean online
config disk c1t3d0s2 copy 1 len=1280 state=clean online
config disk c1t4d0s2 copy 1 len=1280 state=clean online
config disk c1t5d0s2 copy 1 len=1280 state=clean online
config disk c1t6d0s2 copy 1 len=1280 state=clean online

Since the configuration records need to be updated periodically, it is poor practice to replicate configuration records to all devices in large disk groups. Veritas will use the correct number of configuration records by default, so creating additional configuration records is seldom required. For further details on configuration records, take a look at the Veritas Volume Manager administrators guide and vxintro(1m) manual page.