VERITAS Volume Manager 3.5 Administrator's Guide (September 2004)

Administering Dynamic Multipathing (DMP)

Introduction

Chapter 3 109

DMP is also informed when you repair or restore a connection, and when

you add or remove devices after the system has been fully booted

(provided that the operating system recognizes the devices correctly).

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).