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Appendix—Load Balancing 49
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Appendix—Load Balancing
Windows 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, the
driver tries to find a path to the current RAID controller module that owns
the virtual disk. If that path 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
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 49 Thursday, July 18, 2013 5:56 PM