Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

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.
See “RAID-5 (striping with parity)” on page 47.
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.
■ Although hot-relocation does not require you to designate disks as spares,
designate at least one disk as a spare within each disk group. This gives you
some control over which disks are used for relocation. If no spares exist, Veritas
Volume Manager uses any available free space within the disk group. When
Configuring Veritas Volume Manager
Guidelines for configuring storage
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