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

Allows access to the LUNs simultaneously through all the storage ports that are available without significant performance degradation. All the paths are active at all times, 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 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-complaint storage systems provide different levels of access per port. ALUA allows hosts to determine the states of target ports and prioritize paths. The host uses some of the active paths as primary while others as secondary.

Virtual port storage system

Allows access to all available LUNs through a single virtual port. These are active-active storage devices, but hide their multiple connections though a single port. ESXi multipathing does not make multiple connections from a specific port to the storage by default. Some storage vendors supply session managers to establish and manage multiple connections to their storage. These storage systems handle port failover and connection balancing transparently. This is often referred to as transparent failover.