Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Changing the read policy for mirrored volumes
VxVM offers the choice of the following read policies on the data plexes in a
mirrored volume:
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 approach takes advantage of
the drive or controller read-ahead caching policies.
round
Reads first from a plex that has been named as the preferred
plex.
prefer
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.
For disk group versions 150 or higher and if there is a SSD
based plex available, it will be preferred over other plexes.
select
Reads preferentially from plexes at the locally defined site.
This method is the default policy for volumes in disk groups
where site consistency has been enabled.
For disk group versions 150 or higher and if the local site
has a SSD based plex, it will be preferred.
See “About site consistency” on page 469.
siteread
Divides the read requests and distributes them across all
the available plexes.
split
Note: You cannot set the read policy on a RAID-5 volume.
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
Administering volumes
Changing the read policy for mirrored volumes
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