Dell PowerVault MD3000 - Manual (Page 42)

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Post-Installation Tasks
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 these load balance policies to optimize I/O
performance:
• Round robin with subset
• Least queue depth with subset
• Least path weight with subset (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 with Subset
The least queue depth with subset 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 with subset policy treats large block requests and small
block requests equally. The data path selected is in the path group of the
RAID controller module that owns the virtual disk.
Least Path Weight with Subset
The least path weight with subset 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