To ensure server to storage path continuity, we usually deploy redundant physical path components, including NICs (for iSCSI) and HBAs (for FC, SCSI etc). In the event that one or more of these components fails, causing the path to fail, multipathing logic uses an alternate path for I/O so that the servers and applications can still access their data.
Each storage vendor may introduce their own Device Specific Module(DSM) solution, such as PowerPath for EMC. If you did not cater for budget to purchase specific vendor MPIO module, Microsoft did introduce a generic DSM free. I tried it on my W2K8 R2 server on Hyper-V VM and Dell-EMC AX4-5i storage using Round Robin to load balance among the four iSCSI paths. If you are also using W2K8, install MPIO as a feature using Server Manager or "Add-WindowsFeature" cmdlet in Server Core.
Click on Administrative Tools -> MPIO and check on "Add Support for iSCSI devices" on the "Discover Multi-Paths" tab. Reboot the server. On Server Core, you may run
>"mpclaim -r -i -d "MSFT2005iSCSIBusType_0x9""
Invoke iSCSI initiator and connect to the iSCSI targets - make sure that the option "Enable multi-path" is checked. On server core, you may invoke the same initiator using "iscsicpl.exe" command.
Click "Advanced", connect using different path each time. Repeat and rinse for the number of different paths that you have. Click on "Devices" -> "MPIO". And you should the load balancing policy and the multiple paths linking to the Disk devices.
For a more complete Server Core configuration, see "MPIO with Windows 2008 R2 Server Core and iSCSI".
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