HP Veritas Volume Manager 5.0 -UX 11i v3 manual Example of applying load balancing in a SAN

Administering dynamic multipathing (DMP)

Administering DMP using vxdmpadm

# vxdmpadm setattr arrayname DISK iopolicy=singleactive

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Scheduling I/O on the paths of an Asymmetric Active/Active array

You can specify the use_all_paths attribute in conjunction with the adaptive, balanced, minimumq, priority and round-robin I/O policies to specify whether I/O requests are to be scheduled on the secondary paths in addition to the primary paths of an Asymmetric Active/Active (A/A-A) array. Depending on the characteristics of the array, the consequent improved load balancing can increase the total I/O throughput. However, this feature should only be enabled if recommended by the array vendor. It has no effect for array types other than A/A-A.

For example, the following command sets the balanced I/O policy with a partition size of 2048 blocks (2MB) on the enclosure enc0, and allows scheduling of I/O requests on the secondary paths:

#vxdmpadm setattr enclosure enc0 iopolicy=balanced \ partitionsize=2048 use_all_paths=no

The default setting for this attribute is use_all_paths=no.

Example of applying load balancing in a SAN

This example describes how to configure load balancing in a SAN environment where there are multiple primary paths to an Active/Passive device through several SAN switches. As can be seen in this sample output from the vxdisk list command, the device c3t2d15 has eight primary paths:

#vxdisk list c3t2d15

Device: c3t2d15

...

numpaths: 8

c2t0d15 state=enabled type=primary c2t1d15 state=enabled type=primary c3t1d15 state=enabled type=primary c3t2d15 state=enabled type=primary c4t2d15 state=enabled type=primary c4t3d15 state=enabled type=primary c5t3d15 state=enabled type=primary c5t4d15 state=enabled type=primary

In addition, the device is in the enclosure ENC0, belongs to the disk group mydg, and contains a simple concatenated volume myvol1.

The first step is to enable the gathering of DMP statistics:

#vxdmpadm iostat start

Next the dd command is used to apply an input workload from the volume: