VERITAS Volume Manager 3.5 User's Guide - VERITAS Enterprise Administrator (September 2004)

Volume Tasks
VxVM Volumes
Chapter 4106
RAID-5 volume data is interleaved (striped) across three or more
physical disks. Within each stripe across the set of disks, the data on
one of the disks is parity data. If one of the physical disks fails, the
parity data can be used to reconstruct and recover the lost data.
NOTE RAID-5 volumes cannot be mirrored.
Mirrored Volume
Volumes with concatenated or striped layouts can be mirrored to
increase data availability. All of the data in a mirrored volume is
duplicated on at least one other physical disk. If one of the disks
fails, the data can still be accessed from one of the remaining disks.
The plexes in a mirrored volume typically have the same layout, but
a volume can consist of plexes with different layouts. A mirrored
volume has a “mixed” layout if the plexes in the volume have
different layouts.
NOTE You require a licence to mirror disks other than the root disk.
Layered Volume
A layered volume is built on one or more other volumes. The
underlying volumes are typically mirrored. In layered volumes,
mirroring is done at a lower level and with smaller granularity than
with non-layered volumes, so each mirror covers a relatively small
storage region.
Layered volumes tolerate disk failure better than non-layered
volumes and provide improved data redundancy. If a disk in a
layered volume fails, only a portion of the redundancy is lost and
recovery time is usually quicker than it would be for a non-layered
volume. Layered volumes also reduce the chance that two disk
failures will result in lost data.
The underlying volumes in a layered volume are used exclusively by
VxVM and are not intended for user manipulation.
With VxVM, you can create the following types of layered volumes: