VERITAS Volume Manager 4.1 Administrator's Guide

Administering Dynamic Multipathing (DMP)

Load Balancing

Chapter 3 115

Load Balancing

DMP uses the balanced path mechanism to provide load balancing across paths for

active/active disk arrays. Load balancing maximizes I/O throughput by using the total

bandwidth of all available paths. Sequential I/O starting within a certain range is sent down

the same path in order to beneﬁt from disk track caching. Large sequential I/O that does not

fall within the range is distributed across the available paths to reduce the overhead on any

one path.

For active/passive disk arrays, I/O is sent down the primary path. If the primary path fails,

I/O is switched over to the other available primary paths or secondary paths. As the

continuous transfer of ownership of LUNs from one controller to another results in severe I/O

slowdown, load balancing across paths is not performed for active/passive disk arrays.

NOTE Both paths of an active/passive array are not considered to be on different

controllers when mirroring across controllers (for example, when creating a

volume using vxassist make speciﬁed with the mirror=ctlr attribute).

You can use the vxdmpadm command to change the I/O policy for the paths to an enclosure or

disk array as described in “Specifying the I/O Policy” on page 125.