How do I know which host operating system type is correct?

The Host Operating System Type field contains the operating system of the host. You can select the recommended host type from the drop-down list or allow the Host Context Agent (HCA) to configure the host and appropriate host operating system type.

Host Operating System type Operating System (OS) and multipath driver
Factory Default This is reserved for the initial startup of the storage array and should be changed to match the host operating system and multipath driver being used for the particular host
Linux (DM-MP) The Linux OS and the native DM-MP driver
SVC IBM SAN Volume Controller
VMware The ESXi OS
Windows or Windows Clustered The Windows Server OS and Windows MPIO with a DSM driver
After the HCA is installed and the storage is attached to the host, the HCA sends the host topology to the storage controllers through the I/O path. Based on the host topology, the storage controllers automatically define the host and the associated host ports, and then set the host type.
Note: If the HCA does not select the recommended host type, you must manually set the host type.