Definition of a LUN?

Posted on 2009-04-19
Last Modified: 2013-11-14
Hi All,

I was hoping a storage expert could provide me with a definition of a LUN, in terms of SAN?

From what I understand - say you have a a SAN, a LUN is 'virtual partition' of the SAN that you present to one of the servers that accesses the SAN. It is, in effect, a collection of hard disks on the SAN that are spliced together to form a single unit of storage?

Is this correct?
Question by:kam_uk
    LVL 3

    Accepted Solution

    LUN stands for Logical Unit Number: To provide a practical example, a typical disk array has multiple physical SCSI ports, each with one SCSI target address assigned. Then the disk array is formatted as a RAID and then this RAID is partitioned into several separated storage volumes. To represent each volume, a SCSI target is configured to provide a LUN. Each SCSI target may provide multiple LUNs and thus represent multiple volumes, which does not mean that those volumes are concatenated.

    Another example is a single disk drive with one physical SCSI port. It usually provides just a single target, which in turn usually provides just a single LUN numbered zero. This LUN represents the entire storage of the disk drive.

    LVL 3

    Author Comment

    So - was my thinking correct - a LUN is similar to volume presented from a SAN to a server?
    LVL 3

    Expert Comment

    thats exactly how I know it...i've dealt with many LUNS in a server environmet and thats exactly how I preceive them.
    LVL 3

    Expert Comment

    So yes, your thinking is correct
    LVL 7

    Assisted Solution

    I prefere give this definition:

    * Array: one or more disks, in RAIDx policy.
      Usually identified by a name.

    * Logical Volume: a splitted part of full Array, of requested dimension.
      Usually identified by a name.

    * LUN: is an above LV, but associated to 1 or more server(s)
      Usually identified by a number.

    Often, due by different nomenclatures between SAN products,
    last 2 are confused)

    (it may be thinked as the letter in a NTFS partition: the partition exists, in terms of format and size, indipendently from the letter)


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