HP Surestore Auto Path Virtual Array for Windows NT Installation and User's Guide

42 HP Auto Path XP: User’s Guide (Windows NT/2000)
Setting the load balancing policy
The Device Settings window lets you set the load balancing policy for a
selected device.
All of the load balancing policies determine their actions based upon the
current queue depths of all of the paths available to the device. The only
difference between policies is how the queue depth is measured. All of the
policies, except Round Robin, tend to shift the I/O load from heavily loaded
paths or resources to more lightly loaded ones. If the average number of
requests outstanding to the device tends to be small, then all of the policies
behave like the Round Robin policy.
You can select from these load balancing policy options:
No Load Balancing
No load balancing performed. All I/O is routed through
the preferred path. See “Setting the preferred path”
(page 44).
Default Balance Policy
Same as Shortest Queue Service Time.
Round Robin The requests are cycled through each path sequentially
without regard to queue depth.
Shortest Queue Requests
Measures the current queue depth by counting the
number of requests outstanding for each path.
Shortest Queue Bytes
Measures the current queue depth by the sum of the
sizes of the I/O requests outstanding on that path.
Shortest Queue Service Time
(Default) Measures the current queue depth by the sum
of the length of time each I/O request has been
outstanding on that path.