VERITAS Volume Manager 3.5 Administrator's Guide (September 2004)

Performance Monitoring and Tuning

Performance Guidelines

Chapter 12 389

Volume Read Policies

To help optimize performance for different types of volumes, VxVM

supports the following read policies on data plexes:

• round—a round-robin read policy, where all plexes in the volume

take turns satisfying read requests to the volume.

• prefer—a preferred-plex read policy, where the plex with the

highest performance usually satisﬁes read requests. If that plex fails,

another plex is accessed.

• select—default read policy, where the appropriate read policy for

the conﬁguration is selected automatically. For example, prefer is

selected when there is only one striped plex associated with the

volume, and round is selected in most other cases.

NOTE You cannot set the read policy on a RAID-5 data plex. RAID-5 plexes

have their own read policy (RAID).

For instructions on how to conﬁgure the read policy for a volume’s data

plexes, see “Changing the Read Policy for Mirrored Volumes” on

page 279.

In the conﬁguration example shown in the ﬁgure “Use of Mirroring and

Striping for Improved Performance” the read policy of the

mirrored-stripe volume labeled Hot Vol is set to prefer for the striped

plex PL1. This policy distributes the load when reading across the