Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Guidelines for Configuring Storage
450 VERITAS Volume Manager Administrator’s Guide
For more information, see “Striping (RAID-0)” on page 21.
RAID-5 Guidelines
Refer to the following guidelines when using RAID-5.
In general, the guidelines for mirroring and striping together also apply to RAID-5. The
following guidelines should also be observed with RAID-5:
◆ Only one RAID-5 plex can exist per RAID-5 volume (but there can be multiple log
plexes).
◆ The RAID-5 plex must be derived from at least three subdisks on three or more
physical disks. If any log plexes exist, they must belong to disks other than those used
for the RAID-5 plex.
◆ RAID-5 logs can be mirrored and striped.
◆ If the volume length is not explicitly specified, it is set to the length of any RAID-5
plex associated with the volume; otherwise, it is set to zero. If you specify the volume
length, it must be a multiple of the stripe-unit size of the associated RAID-5 plex, if
any.
◆ If the log length is not explicitly specified, it is set to the length of the smallest RAID-5
log plex that is associated, if any. If no RAID-5 log plexes are associated, it is set to
zero.
◆ Sparse RAID-5 log plexes are not valid.
◆ RAID-5 volumes are not supported for sharing in a cluster.
For more information, see “RAID-5 (Striping with Parity)” on page 29.
Hot-Relocation Guidelines
Hot-relocation automatically restores redundancy and access to mirrored and RAID-5
volumes when a disk fails. This is done by relocating the affected subdisks to disks
designated as spares and/or free space in the same disk group.
The hot-relocation feature is enabled by default. The associated daemon, vxrelocd, is
automatically started during system startup.
Refer to the following guidelines when using hot-relocation.
◆ The hot-relocation feature is enabled by default. Although it is possible to disable
hot-relocation, it is advisable to leave it enabled. It will notify you of the nature of the
failure, attempt to relocate any affected subdisks that are redundant, and initiate
recovery procedures.