Logical Unit Number - identifies an individual physical disk or tape device attached to an I/O bus, for example SCSI. If the LUN belongs to a hardware disk array, it might consist of multiple physical disks inside the array, but is not visible outside the array.

A LUN, or logical unit, can either correspond to a single physical disk, or to a collection of disks that are exported as a single logical entity, or virtual disk, by a device driver or by an intelligent disk array’s hardware. VxVM and other software modules may be capable of automatically discovering the special characteristics of LUNs, or you can use disk tags to define new storage attributes. Disk tags are administered by using the <code>vxdisk</code> command or the graphical user interface.