Storage disk systems can be active-active and active-passive.

ESX/ESXi supports the following types of storage systems:

An active-active storage system, which 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.

An active-passive storage system, in which one port is actively providing access to a given LUN. The other ports 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 primary storage port fails, one of the secondary ports or storage processors becomes active, either automatically or through administrator intervention.

A virtual port storage system, which 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. The ESX/ESXi multipathing cannot detect the multiple connections to the storage. These storage systems handle port failover and connection balancing transparently. This is often referred to as transparent failover.