May 30, 2015

vSphere Storage Terminologies - LUN

LUN

LUN – Logical Unit Number – A single block storage allocation presented to a server.

When a host scans the SAN device and finds a block device resource (LUN/disk), it assigns it a unique identifier, the logical unit number.

The term disk is often used interchangeably with LUN.
From the perspective of an ESX host, a LUN is a single unique raw storage block device or disk.

“Though not technically correct, the term LUN is often also used to refer to the logical disk itself.”

In a SAN, storage is allocated in manageable chunks, typically at the logical unit (LUN) level.  These “logical units” are then presented to servers as disk volumes.

A logical unit number (LUN), is a number used to identify a logical unit, which is a device addressed by the SCSI protocol or a Storage Area Network protocol which encapsulate SCSI, such as Fibre Channel or iSCSI.

"To provide a practical example, a typical multi-disk drive has multiple physical SCSI ports, each with one SCSI target address assigned. An administrator may format the disk array as a RAID and then partition this RAID into several separate storage-volumes. To represent each volume, a SCSI target is configured to provide a logical unit. Each SCSI target may provide multiple logical units and thus represent multiple volumes."

For information on identifying disks/LUNs on ESXi: http://kb.vmware.com/kb/1014953

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