VERITAS Volume Manager 3.1 Administrator's Guide

Introduction to Volume Manager
Virtual Object Data Organization (Volume Layouts)
Chapter 146
redundancy.
When striping or spanning across a large number of disks, failure of any
one of those disks can make the entire plex unusable. The chance of one
out of several disks failing is sufficient to make it worthwhile to consider
mirroring in order to improve the reliability (and availability) of a
striped or spanned volume.
Mirroring Plus Striping (RAID-1 + RAID-0)
NOTE You may need an additional license to use this feature.
The Volume Manager supports the combinations of mirroring plus
striping. When used together on the same volume, mirroring plus
striping offers the benefits of spreading data across multiple disks
(striping) while providing redundancy (mirror) of data.
For mirroring plus striping to be effective when used together, the mirror
and its striped plex must be allocated from separate disks. The layout
type of the mirror can be concatenated or striped.
Striping Plus Mirroring (RAID-0 + RAID-1)
NOTE You may need an additional license to use this feature.
The Volume Manager supports the combination of striping with
mirroring. In previous releases, whenever mirroring was used, the
mirroring had to happen above striping. Now there can be mirroring
both above and below striping.
By putting mirroring below striping, each column of the stripe is
mirrored. If the stripe is large enough to have multiple subdisks per
column, each subdisk can be individually mirrored. This layout enhances
redundancy and reduces recovery time in case of an error.
In a mirror- stripe layout, if a disk fails, the entire plex is detached,
thereby losing redundancy on the entire volume. When the disk is
replaced, the entire plex must be brought up to date. Recovering the
entire plex can take a substantial amount of time. If a disk fails in a