Deployment Guide

Load Balancing

Load Balance Policy

Multi-path drivers select the I/O path to a virtual disk through a specific RAID controller module. When

the multi-path driver receives a new I/O to process, the driver tries to find a path to the current RAID

controller module that owns the virtual disk. If the path to the current RAID controller module that owns

the virtual disk cannot be found, the multi-path driver migrates the virtual disk ownership to the

secondary RAID controller module. When multiple paths to the RAID controller module that owns the

virtual disk exist, you can choose a load balance policy to determine which path is used to process I/O.

Multiple options for setting the load balance policies let you optimize I/O performance when mixed host

interfaces are configured.

NOTE: For more information on Load Balance Policy, see your operating system’s manual and

updates.

You can choose one of the following load balance policies to optimize I/O performance:

• Round robin

• Least queue depth

• Least path weight (Microsoft Windows operating systems only)

Round Robin With Subset

The round robin with subset I/O load balance policy routes I/O requests, in rotation, to each available

data path to the RAID controller module that owns the virtual disks. This policy treats all paths to the RAID

controller module that owns the virtual disk equally for I/O activity. Paths to the secondary RAID

controller module are ignored until ownership changes. The basic assumption for the round-robin policy

is that the data paths are equal. With mixed host support, the data paths might have different bandwidths

or different data transfer speeds.

Least Queue Depth

The least queue depth policy is also known as the least I/Os or least requests policy. This policy routes

the next I/O request to a data path that has the least outstanding I/O requests queued. For this policy, an

I/O request is simply a command in the queue. The type of command or the number of blocks that are

associated with the command are not considered.

The least queue depth policy treats large block requests and small block requests equally. The data path

selected is one of the paths in the path group of the RAID controller module that owns the virtual disk.

Least Path Weight

The least path weight policy assigns a weight factor to each data path to a virtual disk. An I/O request is

routed to the path with the lowest weight value to the RAID controller module that owns the virtual disk.