HP MPIO Full Featured DSM for P9000 family of Disk Arrays 4.02.00 installation and reference guide (AA-RVJ6M-TE, October 2010)

NOTE:
• The subset setting is not applicable for devices that have the No Load Balancing policy
enabled.
• The subset setting for a given LUN is persistent across Load Balance policies and host system re-
boots.
• The paths that are part of the subset are reported as "Active" and other paths are reported as
"Available".
You can modify (enable or disable and add or remove paths) the subset setting for a given LUN
through the HP DSM CLI. The current version of HPDSM Manager does not support subset setting
operations. For more information, see Chapter 5.
Use case scenarios
Following are some scenarios where subset based load balance settings are used:
NOTE:
In a host system, for the multipath solution to function properly, all the devices must be accessible
through all the available paths.
1. Using subset setting to group paths for devices based on its usage— When a particular device
has to use only a set of paths for I/O, enable subset for that device to include only the required
paths. This could be used in the following cases:
• When high performing paths are required by devices running critical applications. The other
available paths can be used by non-critical applications.
• When some paths needs to be exclusively used by a particular device, excluding these paths
from the subset members of other devices.
2. Using subset setting during maintenance in a fabric— When a set of components in a fabric (like
switches, and HBAs) are under maintenance and the paths leading through these components
are not to be used for I/O, you can enable subset to exclude the paths for that device until
maintenance is complete.
NOTE:
During maintenance, the subset paths used for I/O must be same for all the devices, else it may result
in I/O errors.
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