Path Selection Plug-Ins (PSPs) are sub plug-ins of the VMware NMP and are responsible for choosing a physical path for I/O requests.

The VMware NMP assigns a default PSP for each logical device based on the SATP associated with the physical paths for that device. You can override the default PSP. For information, see Path Scanning and Claiming.

By default, the VMware NMP supports the following PSPs:

VMW_PSP_MRU

The host selects the path that it used most recently. When the path becomes unavailable, the host selects an alternative path. The host does not revert back to the original path when that path becomes available again. There is no preferred path setting with the MRU policy. MRU is the default policy for most active-passive storage devices.

The VMW_PSP_MRU ranking capability allows you to assign ranks to individual paths. To set ranks to individual paths, use the esxcli storage nmp psp generic pathconfig set command. For details, see the VMware knowledge base article at http://kb.vmware.com/kb/2003468.

The policy is displayed in the client as the Most Recently Used (VMware) path selection policy.

VMW_PSP_FIXED

The host uses the designated preferred path, if it has been configured. Otherwise, it selects the first working path discovered at system boot time. If you want the host to use a particular preferred path, specify it manually. Fixed is the default policy for most active-active storage devices.

Note

If the host uses a default preferred path and the path's status turns to Dead, a new path is selected as preferred. However, if you explicitly designate the preferred path, it will remain preferred even when it becomes inaccessible.

Displayed in the client as the Fixed (VMware) path selection policy.

VMW_PSP_RR

The host uses an automatic path selection algorithm rotating through all active paths when connecting to active-passive arrays, or through all available paths when connecting to active-active arrays. RR is the default for a number of arrays and can be used with both active-active and active-passive arrays to implement load balancing across paths for different LUNs.

Displayed in the client as the Round Robin (VMware) path selection policy.