For a mirrored volume, Veritas Volume Manager (VxVM) uses the read policy to determine which data plex in the volume to use for reads. By default, VxVM chooses a plex using the following criteria, in order:
Site
Plexes on the same site are chosen over plexes on another site.
Connectivity
Locally connected plexes are chosen over remotely connected plexes. This criterion applies for shared disk groups.
Media type
SSD devices are chosen over HDDs.
Layout
Striped plexes are chosen over other layouts
To customize the read policy, you can choose one of the following VxVM read policies:
To set the read policy to round, use the following command:
# vxvol [-g diskgroup] rdpol round volume
For example, to set the read policy for the volume vol01 in disk group mydg to round-robin, use the following command:
# vxvol -g mydg rdpol round vol01
To set the read policy to prefer, use the following command:
# vxvol [-g diskgroup] rdpol prefer volume preferred_plex
For example, to set the policy for vol01 to read preferentially from the plex vol01-02, use the following command:
# vxvol -g mydg rdpol prefer vol01 vol01-02
To set the read policy to select, use the following command:
# vxvol [-g diskgroup] rdpol select volume