In the ESXi context, the term target identifies a single storage unit that the host can access. The terms storage device and LUN describe a logical volume that represents storage space on a target. In the ESXi context, both terms also mean a storage volume that is presented to the host from a storage target and is available for formatting. Storage device and LUN are often used interchangeably.

Different storage vendors present the storage systems to ESXi hosts in different ways. Some vendors present a single target with multiple storage devices or LUNs on it, while others present multiple targets with one LUN each.

Figure 1. Target and LUN Representations
In one example, the host sees one target with three LUNs. In the other example, the host sees three targets with one LUN each.

In this illustration, three LUNs are available in each configuration. In one case, the host connects to one target, but that target has three LUNs that can be used. Each LUN represents an individual storage volume. In the other example, the host detects three different targets, each having one LUN.

Targets that are accessed through the network have unique names that are provided by the storage systems. The iSCSI targets use iSCSI names. Fibre Channel targets use World Wide Names (WWNs).
Note: ESXi does not support accessing the same LUN through different transport protocols, such as iSCSI and Fibre Channel.

A device, or LUN, is identified by its UUID name. If a LUN is shared by multiple hosts, it must be presented to all hosts with the same UUID.