Erik,

I haven't seen anything similar before.

I think there is a lot of information required before we could understand the situation like what hypervisor and storage is being used, etc. In addition, we'll need to thoroughly look at the management server and hypervisor logs to find out exactly what happened.

I recommend engaging Citrix support to troubleshoot this further.

Regards,
Somesh

What do you mean by volume gone? The volume of the instance was restored to the default template?

What is the primary storage in your environment? Is it local storage?

The issue ( root volume restored to original template) can happen if someone has performed the resetVM operation from CloudPlatform UI. To confirm this look at the entries in the event table.

mysql> select * from event where type='VM.RESTORE';

If you see any entries from the above query then it indicates that the resetVM was done on few VM's. Unfortunately from the entries you cannot confirm the VM on which the resetVM was done but you can look at the date in created column to see if it matches when the issue was reported by your users

Erik --> It would be helpful if I could revie a historical record of which instance a volume USED to be attached to.

You may have the historical record in cloud DB if the volume was replaced as a part of resetVM operation, but the GC on the xenserver might have already destroyed the old volume

You can try the following query

select * from volumes where name='ROOT-#';

Replace # with the Id of the VM, look for the value in "path" column from the above output, this will give you the name of the VHD that were used as ROOT volumes. The entry with removed column as null indicates that it is currently being used.