Lvm – is it possible to simultaneously mount 2 LVM volumes that are exact copies of each other (same UUIDs)

lvmuuid

I have cloned (using dd) the hard drive in a live system onto several multiple backup hard drives. The root partition in the live system is a LVM volume. The backup copies are intended to be drop-in replacements for the original and this means they need to have the same UUID as the master.

Quick question: is it possible to mount one of the backup HDs on the live system? When I try to do so LVM is understandably confused about this due to the same UUIDs and volume group names. Following the hint found in [this answer][1] to first rename the original LVM group, I have tried:

  1. connecting the external backup HD into a USB port

  2. running (note that the string 'test' is the group name on this system)

# vgrename test test-live
Volume group "test" successfully renamed to "test-live"
vgscan --mknodes
Reading all physical volumes.  This may take a while...
Found duplicate PV qWUadGaM2MU1UAJ5Spp8upD6fbddk7Zb: using /dev/dm-3 not /dev/dm-0
Found volume group "test" using metadata type lvm2
# vgchange -ay
Found duplicate PV qWUadGaM2MU1UAJ5Spp8upD6fbddk7Zb: using /dev/dm-3 not /dev/dm-0
2 logical volume(s) in volume group "test" now active

At this point I would have expected to have been able to access the individual logical volumes under /dev/test/. Running lvdisplay produces. 

Found duplicate PV qWUadGaM2MU1UAJ5Spp8upD6fbddk7Zb: using /dev/dm-3 not /dev/dm-0

  --- Logical volume ---
  LV Name                /dev/test/root
  VG Name                test
  LV UUID                UuKUH3-yzPo-CbOz-tU4B-W6om-qdMn-0XSNZU
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                126.48 GiB
  Current LE             32378
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           252:1

  --- Logical volume ---
  LV Name                /dev/test/swap_1
  VG Name                test
  LV UUID                OGJhJu-QByo-6AzG-sk1x-jh3e-dU9L-sHk91t
  LV Write Access        read/write
  LV Status              available
  # open                 2
  LV Size                3.90 GiB
  Current LE             999
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           252:2

However, /dev/test/ does not exist at all and therefore I cannot access the logical volumes at /dev/test/root and /dev/test/swap_1 as lvdisplay suggested.

Best Answer

The whole point of UUIDs is to uniquely identify something, and what you're trying to do makes them non-unique. I highly doubt that this is possible. I played around with pvchange -u to change the UUID of a duplicated PV, but the operation always failed.

If you really need to mount the backups on the live host, I suggest that you backup the LVs individually (i.e. create a new PV, VG and LVs on the backup device and dd each LV separately).

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