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Veritas™ Volume Manager Administrator's Guide

Last Published: 2018-11-02

Product(s): InfoScale & Storage Foundation (5.1 SP1)

Platform: HP-UX

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 approach 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. For disk group versions 150 or higher and if there is a SSD based plex available, it will be preferred over other plexes.
siteread	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.
split	Divides the read requests and distributes them across all the available plexes.

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

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

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