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VM disk recovery procedure from lun snapshot

Sandro Bordacchini



I have a small vitualization infrastructure: 2 Dell servers with XenServer 6.5 90233c and 1 QNAP NAS as iSCSI target (LVM over iSCSI) for storage.

I have about 12 VMs running on the infrastructure. Storage is provided by two LUNs on the QNAP (2TB each, one thick provisioned, other think provisioned), mapped as two SRs.

LUN snapshots are taken periodically on the NAS and moved to another QNAP nas, let's call it "backup" nas.

I need to restore one VM disk. I found a suitable lun snapshot on the backup nas. Of course I cannot restore all the LUN snapshot, since the other VMs there are fine.


I thought I could:

  1. select and mount a LUN snapshot as iSCSI target on the backup nas (DONE)
  2. attach the iSCSI target to the pool via XenCenter (7.1)
  3. grab the wanted disk file from the iSCSI target (on the backup nas) and move it on the pool storage (local or main NAS)
  4. shutdown the VM and somehow replace the failed disk file with the recovered one


Unfortunately I got an error while doing the second step (see attached file).
I suppose this is due to the fact that the mounted lun snapshot has the same uuid of the "source" SR.

Before continuing trying... I wonder if someone can point me to a procedure/tutorial/howto to do a restore of a single VM starting from a lun snapshot.

Thanks in advance.




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You probably only have two choicess: 1) temporarily detach the current iSCSI LUN associated with that SR to be able to bring in the snapshot version and then move the VM to local storage temporraily before reversing the process, or 2) attach the LUN to an unrelated host or pool to be able to pull in the VM.


Doing a periodic vm-export on your VMs would be a way to avoid this conflict in the future.



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9 minutes ago, Tobias Kreidl said:


That GitHub VmBackup utility is certainly one option. There are a number of other both commercial and free backup utilities out there, but having some sort of a backup means

in place and active is highly recommended.


I definitely agree with you.
I thought I was covered with the lun snapshot, but i made the biggest error after not having a backup, i.e. not trying a restore :-)
Feel free to suggest me any other free backup tool.



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