Deployment Guide
Load balancing
Load balance policy
Multi-path drivers select the I/O path to a virtual disk through a specic RAID controller module. When the multi-path driver receives a new
I/O to process, the driver tries to nd 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 congured.
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 dierent bandwidths or dierent 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. If more than one data path to the virtual disk has the same weight
value, the round robin with subset path selection policy is used to route I/O requests between the paths with the same weight value. The
least path weight load balance policy is not supported on Linux operating systems.
5
Load balancing 25