8x00 family of Disk Arrays 4.01.00 installation and reference guide (AA-RW7SP-TE, September 2010)

NOTE:

• All devices that are part of the logical unit group, have the same subset setting.

• 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 4.

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.

Adaptive Load Balance

The HP MPIO EVA DSM implements array specific load balancing algorithms that utilize certain

features supported by the disk arrays, to deliver better performance for host I/O requests. The Adaptive

Load Balance (ALB) setting is supported on a per logical unit basis and works in conjunction with the

load balancing policies supported by the DSM.

By default, ALB is disabled for the newly discovered LUN. If the newly discovered LUN is part of any

logical unit group, the ALB setting of the existing group prevails.

Load balancing20