Appendix—Load Balancing 77
C

Appendix—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.
You can choose one of the following load balance policies to optimize I/O
performance:
• Round robin with subset
• Least queue depth with subset
• Least path weight with subset (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.
book.book Page 77 Sunday, September 11, 2011 10:24 PM