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

Appendix B, Configuring VERITAS Volume Manager
Guidelines for Configuring Storage
451
◆ 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 free space is used for relocation
purposes, it is possible to have performance degradation after the relocation.
◆ After hot-relocation occurs, designate one or more additional disks as spares to
augment the spare space. Some of the original spare space may be occupied by
relocated subdisks.
◆ If a given disk group spans multiple controllers and has more than one spare disk, set
up the spare disks on different controllers (in case one of the controllers fails).
◆ For a mirrored volume, configure the disk group so that there is at least one disk that
does not already contain a mirror of the volume. This disk should either be a spare
disk with some available space or a regular disk with some free space and the disk is
not excluded from hot-relocation use.
◆ For a mirrored and striped volume, configure the disk group so that at least one disk
does not already contain one of the mirrors of the volume or another subdisk in the
striped plex. This disk should either be a spare disk with some available space or a
regular disk with some free space and the disk is not excluded from hot-relocation
use.
◆ For a RAID-5 volume, configure the disk group so that at least one disk does not
already contain the RAID-5 plex (or one of its log plexes) of the volume. This disk
should either be a spare disk with some available space or a regular disk with some
free space and the disk is not excluded from hot-relocation use.
◆ If a mirrored volume has a DRL log subdisk as part of its data plex, you cannot
relocate the data plex. Instead, place log subdisks in log plexes that contain no data.
◆ Hot-relocation does not guarantee to preserve the original performance characteristics
or data layout. Examine the locations of newly-relocated subdisks to determine
whether they should be relocated to more suitable disks to regain the original
performance benefits.
◆ Although it is possible to build VERITAS Volume Manager objects on spare disks
(using vxmake or the VEA interface), it is recommended that you use spare disks for
hot-relocation only.
See “Administering Hot-Relocation” on page 327 for more information.