In some storage configurations, it is possible to have multiple paths from the server to the storage. This is often done for redundant paths or higher bandwidth. Typically multipathing is used in Fibre Channel SANs, in SAS attached storage and in some iSCSI connections.
When there is a multipath configuration, Windows Disk Magagment tool will show the same device multiple times. In the example below the same LUN is seen 4 times by Windows Server.
But there is only (1) LUN. It will be necessary to enable Windows MPIO to see only that one LUN.
Enabling Windows MPIO
To enable Windows MPIO , from the Server Manager select Add Roles and Features.
MPIO is a feature, click Next until you get to the features. Scroll down and enable MPIO.
Click Next and click the Install button.
Once the install is complete, close the Wizard and reboot the server.
Once the server is booted, click the Start menu and type in MPIO
Click MPIO to open the MPIO applet. Select the Discover Multi-Paths tab on top, select the Promise device in Others and click Add.
Another restart will be required. After the reboot the Disk Management tool shows only one disk.
To change the pathing policy open the device manager and select properties for the multipath promise LUN.
Select the MPIO tab at the top and the drop-down menu shows the pathing policies Windows supports.
For best bandwith Least Queue Depth is suggested.
iSCSI multipathing is an option in the MPIO applet. Select the Discover Multi-Paths tab and click Add Support for iSCSI devices. Another reboot will be required.