XenServer snapshot changes the disk UUID

[Marcel Zunnebeld]

Hello,

In an automated image (Ivanti Automation) process I create a new vDisk of a VM from a base snapshot (snapshot 1).
Then some applications are installed and another snapshot of the VM is made (snapshot2 ).
To then proceed with a custom installation, I resize the disk and take another snapshot (snapshot 3). That all goes fine, but when I want to go back to snapshot 2, the UUID of the disk has changed compared to snapshot 1 and my scripts that deal with commands for the disk no longer work.

Does anyone know if you can leave the UUID fixed? Or how to read the UUID from a disk and put it in a parameter?

Thanks in advance!

[Tobias Kreidl]

The UUID of the disk is fixed and cannot be changed.

I'd suggest copying the current VDI to a new VDI, detaching the current VDI, and attaching the new VDI to the VM. Then if all is well, you can delete the old VDI along with its snapshots. I strongly suspect that growing the storage in the middle of a snapshot chain messed things up. At least then you could start with a "clean" VDI and start taking valid snapshots once again.

The caveat is that you'll probably have to shut down the VM to accomplish this.

 

-=Tobias

[Marcel Zunnebeld]

Hi Tobias, thank you for your comment.

The UUID of the disk is not completely fixed. It changes when you do a revert ?
And that's exactly where the problem lies, then the script can no longer be used.
Hopefully there is another solution for this?

[Tobias Kreidl]

Right, it will always be unique whenever it's recreated and it will be auto-generated, and cannot be changed! Is there a way you can figure out within your script what the new UUID is? Is there maybe away to accomplish what you need to do using instead some other parameter to identify the storage?

 

-=Tobias

[Marcel Zunnebeld]

Hi Tobias, thanks. I'm still looking for that way of reading out the new UUID and then using it as a parameter. Another possibility can be based on snapshot name or something like that. I'm going to test with that next week (didn't get to it this week due to a flu).

[Tobias Kreidl]

Not sure what you mean by "using it [the UUID] as a parameter" --  a parameter with what purpose?

Once created, you can of course query the UUID of the VDI, but not before it exists. See, for example:

https://linuxconfig.org/how-to-rename-vdi-virtual-disk-on-xenserver-linux

 

-=Tobias

[Marcel Zunnebeld]

Hi Tobias, apologies, I meant a variable instead of a parameter.
 

I need only the UUID itself to store as a variable in a .sh script from this output or any output like it that has a UUID:

Command:
xe snapshot-list name-label="snapshot2"

 

With the PowerShell command
Get-XenVM | Where {$_.is_a_snapshot -eq $True} | select name_label i do get the snapshot names, and with
Get-XenVM | Where {$_.is_a_snapshot -eq $True} | select uuid  i do get the UUIDs

But I want to request the UUID of eg snapshot2 to store that as a variable in a .sh script

[Tobias Kreidl]

See if this helps. Sorry, I do not do any PowerShell. https://serverfault.com/questions/957186/storing-xenserver-vm-snapshot-uuid-as-a-variable-in-a-shell-script-to-create-xv

[Tobias Kreidl]

I know this is a really old document but it's very good and mostly still accurate. It's an excellent guide to the fundamentals of XenServer networking.

 

https://www.irya.unam.mx/computo/sites/manuales/xenserver/XS-design-network_advanced.pdf

 

-=Tobias

[Marcel Zunnebeld]

Hi Tobias,

Thanks for the hint to the article.
With some trial and error it finally worked. I now have the following script which does exactly what it should:

xe vm-disk-list vm=<VMName>
xe vm-disk-list vm=<VMName> | grep -B 1 -A 1 "<name-label name of Disk 0 VDI>"

Then:

uuid=`xe vm-disk-list vm=<VMName> | grep -B 1 -A 1 "<name-label name of Disk 0 VDI>"| awk '/uuid/ {print $5}'`
xe vdi-resize disk-size=131GiB uuid=$uuid
 

For a VM named W10-GM-2 and a Disk 0 VDI name-label of W10-GM_2 0 it would be:
 

uuid=`xe vm-disk-list vm=W10-GM-2 | grep -B 1 -A 1 "W10-GM_2 0"| awk '/uuid/ {print $5}'`
xe vdi-resize disk-size=131GiB uuid=$uuid

Thanks for your help in this!