Changing the Read Policy for Mirrored Volumes

VxVM offers the choice of the following read policies on the data plexes in a mirrored volume:

• round reads each plex in turn in "round-robin" fashion for each nonsequential I/O detected. Sequential access causes only one plex to be accessed. This takes advantage of the drive or controller read-ahead caching policies.
• prefer reads first from a plex that has been named as the preferred plex.
• select chooses a default policy based on plex associations to the volume. If the volume has an enabled striped plex, the select option defaults to preferring that plex; otherwise, it defaults to round-robin.

The read policy can be changed from round to prefer (or the reverse), or to a different preferred plex. The vxvol rdpol command sets the read policy for a volume.

To set the read policy to round, use the following command:

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

To set the read policy to prefer, use the following command:

For example, to set the policy for vol01 to read preferentially from the plex vol01-02, use the following command:

To set the read policy to select, use the following command:

For more information about how read policies affect performance, see Volume Read Policies.