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Mounting a Root Partition in a Logical Volume

Novell Cool Solutions: Tip
By Ren Purcell

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Posted: 28 Sep 2007
 

Problem:

You have created a Logical Volume to receive a Xen VM. During the VM installation you created two partitions inside the LV, one swap and one for the root and you want to mount the root partition inside the LV.

So it looks like this:

sda (physical disk)
  sda1 ( / Dom0 )
  sda2 ( swap Dom0 )
  sda3 (partition system id=8e LVM)
      VG1
         LV1 DomU (virtual hda for the Xen VM)
             sda1 ext3 /
             sda2 swap

Solution:

You need to know the exact starting point of the partition inside your LV to mount it.

Example:

There's a partition table in: /dev/vg1/lv1

With this command you can see the partition contained in your LV

-----------------------------------------------------------------------------
fdisk -l -u /dev/vg1/lv1

"Don't forget the "-u" it's important this will show you the size in sector"

Disk /dev/vg1/lv1: 4294 MB, 4294967296 bytes
255 heads, 63 sectors/track, 522 cylinders, total 8388608 sectors
Units = sectors of 1 * 512 = 512 bytes

        Device Boot      Start         End      Blocks   Id  System
/dev/vg1/lv1p1              63      899639      449788+  82  Linux
swap / Solaris
/dev/vg1/lv1p2   *      899640     8385929     3743145   83  Linux
-----------------------------------------------------------------------------

Now if you want to mount the second partition in your LV type:

mount -o loop,offset=460615680 /dev/vg1/lv1p2 /mnt/vm01

460615680 is equal to 899640 * 512 (512 are the size of each sector and 899640 the starting point of the partition. (You can get these numbers with the fdisk command..)

Special thanks to Jean-Francois Saucier for the tips.

Environment:

  • SUSE Linux Enterprise Server
  • Xen
  • LVM


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