Difference between volume, partition and lun

Posted on 2014-07-15
Last Modified: 2014-07-22
What is the difference between a volume, partition and lun? How do they relate (or not) to each other? If there is a diagram available to explain it better that would be great
Question by:marvinbautista
    LVL 46

    Assisted Solution

    A volume can be a logical or physical entity like a physical disk drive, or a 2-disk RAID1 set.  This volume is sliced into 1 or more logical partitions.  Each partition would generally have a filesystem on it.  In the windows terminology you would  take a volume, partition that volume into a C and E drive.  

    A LUN is  computer-speak for the identifier name or number assigned by the hardware + O/S for the logical volume.

    The disk controller and BIOS deals with volumes by their LUN, those things are unaware and don't care about partitions.
    LVL 11

    Assisted Solution

    by:N R
    LUN is a logical disk as created on SAN storage array and is assigned to host in SAN using LUN binding, It appears on the host as local disk.
    Storage array usually have large storage capacity, we don't want one  server to use the whole thing, so we divide it into logical units (LUN) is actually Logical Unit Number, so we get storage sliced into usable chunks, and present  it to the server. In a simple example, suppose it shows up as local disk on server just like /dev/sdc.

    Volume We carve out volume using one or more LUNs (storage disks from OS's view) We want to be able to add more space or shrink the space. volume makes it possible. We can resize that LUN on the  storage array (or even create another LUN and present that to the  server) and using LVM (Logical Volume Manager), We can grow the volume without rebooting.There are several good features like cloning, mirroring, high availability etc.of volumes.
    LVL 25

    Accepted Solution

    a LUN is a logical disk created on a SAN.
    it can actually be a physical disk, a raid array of physical disks, a raid array of partitions of physical disks, a partition of a single disk...

    a volume is a storage device in the OS.
    LUNs, physical disk drives, iSCSI exports, ... are volumes from the OS's perspective.
    volumes can either be sliced and/or partitioned, or used like one would use a partition (see below).

    a partition is a fraction of a volume.
    volumes can be partitioned in various ways (gpt for example). usually, a single partition contains a single filesystem. partitions can also be used in other various ways such as raw space for specific applications such as database engines, raw space for a virtual machine (in that case, the guest OS will "see" that partition as a volume), swap space...


    to make things simple, most OSes nowadays implement logical volume managers which have the ability to combine volumes and/or partitions (and sometimes files) in order to create logical volumes.

    to make things even simpler, software such as zfs or btrfs combine the feature of volume managers and filesystem. they can create data pools (which are more or less the equivalent of logical volumes) out of a combination of mostly anything that looks like data storage, and create multiple parallel filesystems in those pools without partitioning them.

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