Figure 3 Multi-site SAN VIPs with MPIO
Setting the Microsoft DSM MPIO load balancing policy
When you connect application servers to volumes, you can also set the MPIO load balancing
policy in the iSCSI Initiator.
Supported load balancing options
Only two load balancing options are supported, Fail Over and Round Robin. For the Microsoft
DSM with Windows 2003 Server, only the Fail Over Only option is supported.
• Fail Over Only – Also called active/passive MPIO. Two (or more) I/O paths are built between
the server and the storage. One path is actively used for I/O to the storage. The other paths
are available for failover only in the event the primary path goes down.
• Round Robin – Also called active/active MPIO. Two (or more) I/O paths are built between
the server and the storage. All paths are actively used for I/O to the storage.
In the DSM for MPIO, Vendor Specific is selected by default. This option is the same as selecting
Fail Over Only and will not be available after you select another option. In the Microsoft DSM,
Fail Over Only is the default selection for all Windows versions, except for Windows 2008 R2,
for which Round Robin is the default.
The MPIO load balancing policy affects the number of iSCSI connections created to the volume.
The number of connections also differs based on whether you are using the DSM for MPIO or the
Microsoft DSM. “DSM for MPIO with two NICs in the server and Failover MPIO load balancing”
(page 8) through “Microsoft DSM with two NICs in the server and Round Robin MPIO load
balancing” (page 9) show the connections created with applications servers that have two NICs.
Figure 4 DSM for MPIO with two NICs in the server and Failover MPIO load balancing
8 Using MPIO
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