VxVM Change the read-policy

What are the read policies for plexes in VERITAS Volume Manager?

When a volume has more than one enabled associated plex, VERITAS Volume Manager (VxVM) can distribute reads between the plexes to distribute the I/O load and thus increase total possible bandwidth of reads through the volume. The read policy can be set by the administrator. Possible policies are:

1. Preferred plex
This read policy specifies a particular named plex that is used to satisfy read requests. In the event that a read request cannot be satisfied by the preferred plex, this policy changes to round-robin.
2. Round-robin
For every other read operation, distribute the operation across all of the available plexes. Given three plexes, this switches between each of the three plexes, so each plex gets one third of the read requests.
3. Select
This read policy is the default policy, and adjusts to use an appropriate read policy based on the set of plexes associated with the volume. If exactly one enabled read-write striped plex is associated with the volume, then that plex is chosen automatically as the preferred plex; otherwise, the round-robin policy is used. If a volume has one striped plex and one non-striped plex, preferring the striped plex often yields better throughput.

To change the read-policy to a volume, use the following command:

# vxvol -g rdpol

For example, to set the read policy for volume vol01 in disk group datadg to round-robin, use the following command:

# vxvol -g datadg rdpol round vol01