For each storage device, the ESX/ESXi host sets the path selection policy based on the claim rules defined in the /etc/vmware/esx.conf file.

By default, VMware supports the following path selection policies. If you have a third-party PSP installed on your host, its policy also appears on the list.

Fixed (VMware)

The host always uses the preferred path to the disk when that path is available. If the host cannot access the disk through the preferred path, it tries the alternative paths. The default policy for active-active storage devices is Fixed.

Most Recently Used (VMware)

The host uses a path to the disk until the path becomes unavailable. When the path becomes unavailable, the host selects one of the alternative paths. 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 active-passive storage devices and is required for those devices.

Round Robin (VMware)

The host uses an automatic path selection algorithm rotating through all available paths. This implements load balancing across all the available physical paths.

Load balancing is the process of spreading server I/O requests across all available host paths. The goal is to optimize performance in terms of throughput (I/O per second, megabytes per second, or response times).

Path Policy Effects summarizes how the behavior of host changes, depending on the type of array and the failover policy.

Path Policy Effects

Policy/Controller

Active-Active

Active-Passive

Most Recently Used

Administrator action is required to fail back after path failure.

Administrator action is required to fail back after path failure.

Fixed

VMkernel resumes using the preferred path when connectivity is restored.

VMkernel attempts to resume using the preferred path. This can cause path thrashing or failure when another SP now owns the LUN.

Round Robin

No fail back.

Next path in round robin scheduling is selected.