VERITAS Volume Manager 3.1 Administrator's Guide

Initialization and Setup
System Setup Guidelines
Chapter 276
NOTE Many modern disk drives have “variable geometry,” which means that
the track size differs between cylinders (i.e., outer disk tracks have
more sectors than inner tracks). It is therefore not always appropriate
to use the track size as the stripe unit size. For these drives, use a
moderate stripe unit size (such as 64 kilobytes), unless you know the
I/O pattern of the application.
• Volumes with small stripe unit sizes can exhibit poor sequential I/O
latency if the disks do not have synchronized spindles. Generally,
striping over non-spindle-synched disks performs better if used with
larger stripe unit sizes and multi-threaded, or largely asynchronous,
random I/O streams.
• Typically, the greater the number of physical disks in the stripe, the
greater the improvement in I/O performance; however, this reduces
the effective mean time between failures of the volume. If this is an
issue, striping can be combined with mirroring to provide a
high-performance volume with improved reliability.
• If only one plex of a mirrored volume is striped, be sure to set the
policy of the volume to prefer for the striped plex. (The default read
policy, select, does this automatically.)
• If more than one plex of a mirrored volume is striped, make sure the
stripe unit size is the same for each striped plex.
• Where possible, distribute the subdisks of a striped volume across
drives connected to different controllers and buses.
• Avoid the use of controllers that do not support overlapped seeks
(these are rare).
The vxassist command automatically applies and enforces many of
these rules when it allocates space for striped plexes in a volume.
Mirroring Guidelines
NOTE You must license the VERITAS Volume Manager product to use this
feature.