Path Selection Plug-Ins (PSPs) run with 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.

By default, the VMware NMP supports the following PSPs:

Most Recently Used (VMW_PSP_MRU)

Selects the path the ESX host used most recently to access the given device. If this path becomes unavailable, the host switches to an alternative path and continues to use the new path while it is available. MRU is the default path policy for active-passive arrays.

Fixed (VMW_PSP_FIXED)

Uses the designated preferred path, if it has been configured. Otherwise, it uses the first working path discovered at system boot time. If the host cannot use the preferred path, it selects a random alternative available path. The host reverts back to the preferred path as soon as that path becomes available. Fixed is the default path policy for active-active arrays.

Caution

If used with active-passive arrays, the Fixed path policy might cause path thrashing.

VMW_PSP_FIXED_AP

Extends the Fixed functionality to active-passive and ALUA mode arrays.

Round Robin (VMW_PSP_RR)

Uses a path selection algorithm that rotates through all available active paths enabling load balancing across the paths.