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515Configuring Veritas Volume Manager
Guidelines for configuring storage
Dirty region logging guidelines
Dirty region logging (DRL) can speed up recovery of mirrored volumes following
a system crash. When DRL is enabled, Veritas Volume Manager keeps track of
the regions within a volume that have changed as a result of writes to a plex.
Note: Using Dirty Region Logging can impact system performance in a write-
intensive environment.
For more information, see “Dirty region logging” on page 60.
Striping guidelines
Refer to the following guidelines when using striping.
■ 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 vxassist) 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, use the default stripe-unit size.
Note: Many modern disk drives have variable geometry. This means that the
track size differs between cylinders, so that 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 disks
without synchronized spindles yields better performance when 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, combine
striping with mirroring to combine high-performance with improved
reliability.
■ If only one plex of a mirrored volume is striped, set the policy of the volume
to prefer for the striped plex. (The default read policy, select, does this
automatically.)