VERITAS Volume Manager 3.1 Administrator's Guide

Performance Monitoring
Performance Guidelines:
Chapter 9 393
30 percent writes), then mirroring can result in somewhat reduced
performance.
To provide optimal performance for different types of mirrored volumes,
Volume Manager supports these read policies:
The round-robin read policy (round), where read requests to the
volume are satisfied in a round-robin manner from all plexes in the
volume.
The preferred-plex read policy (prefer), where read requests are
satisfied from one specific plex (presumably the plex with the highest
performance), unless that plex has failed, in which case another plex
is accessed.
The default read policy (select), which selects the appropriate read
policy for the configuration. For example, selecting preferred-plex
when there is only one striped plex associated with the volume and
round-robin in most other cases.
In the configuration example shown in Figure 9-2, Use of Mirroring and
Striping for Improved Performance, the read policy of the volume labeled
Hot Vol should be set to prefer for the striped plex labeled PL1. In this
way, reads going to PL1 distribute the load across a number of otherwise
lightly-used disks, as opposed to a single disk.
Figure 9-2 Use of Mirroring and Striping for Improved Performance
To improve performance for read-intensive workloads, up to 32 plexes
can be attached to the same volume. However, this scenario results in a
Disk 1 Disk 2 Disk 3 Disk 4
Hot Vol
PL1 SD1
Hot Vol
PL1 SD2
Hot Vol
PL1 SD3
Hot Vol
PL2 SD1
Lightly
Used
Area
Lightly
Used
Area
Lightly
Used
Area
Used
Area