VERITAS Volume Manager 3.1 Administrator's Guide

Initialization and Setup
System Setup Guidelines
Chapter 2 75
one disk that 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, the disk group must have at least one disk that
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,
that plex cannot be relocated. You can place log subdisks in plexes
that contain no data (log plexes).
• Hot-relocation does not guarantee that it preserves the original
performance characteristics or data layout. You can examine the
location(s) of the newly-relocated subdisk(s) and determine whether
they should be relocated to more suitable disks to regain the original
performance benefits.
• Hot-relocation is capable of creating a new mirror of the root disk if
the root disk is mirrored and it fails. The rootdg disk group should
therefore contain sufficient contiguous spare or free space to
accommodate the volumes on the root disk (rootvol and swapvol
require contiguous disk space).
• Although it is possible to build VxVM objects on spare disks (using
vxmake or the Storage Administrator interface), it is preferable to use
spare disks for hot-relocation only.
Striping Guidelines
Follow these general guidelines when using striping. See “Striping
(RAID-0)” for more information.
• Do not place more than one column of a striped plex on the same
physical disk.
• Calculate stripe unit sizes carefully. In general, a moderate stripe
unit size (for example, 64 kilobytes, which is also the default used by
the vxassist command) is recommended. If it is not feasible to set
the stripe unit size to the track size, and you do not know the
application I/O pattern, it is recommended that you use 64 kilobytes
for the stripe unit size.