ESXi supports different storage systems and arrays.

The types of storage that your host supports include active-active, active-passive, and ALUA-compliant.

Active-active storage system

Supports access to the LUNs simultaneously through all the storage ports that are available without significant performance degradation. All the paths are active, unless a path fails.

Active-passive storage system

A system in which one storage processor is actively providing access to a given LUN. The other processors act as a backup for the LUN and can be actively providing access to other LUN I/O. I/O can be successfully sent only to an active port for a given LUN. If access through the active storage port fails, one of the passive storage processors can be activated by the servers accessing it.

Asymmetrical storage system

Supports Asymmetric Logical Unit Access (ALUA). ALUA-compliant storage systems provide different levels of access per port. With ALUA, the host can determine the states of target ports and prioritize paths. The host uses some of the active paths as primary, and uses others as secondary.