mike-tutkowski commented on issue #2298: CLOUDSTACK-9620: Enhancements for 
managed storage
URL: https://github.com/apache/cloudstack/pull/2298#issuecomment-356746715
 
 
   @rafaelweingartner Yeah, sorry if I wasn't clear about that back when we 
were looking at your PR.
   
   For XenServer + managed storage, there are two approaches to taking volume 
snapshots:
   
   1) The volume snapshot resides on primary storage.
   
   2) The volume snapshot goes through a SAN snapshot and ends up on secondary 
storage.
   
   In use case one, a snapshot is created on the SAN (fast and space efficient, 
but it's not technically a backup). To make use of it (i.e. to create a volume 
from a volume snapshot or a template from a volume snapshot) on XenServer, we 
can leverage UUID resigning (if the applicable XenServer service pack is 
installed). If UUID resigning is not available (because the service pack isn't 
installed), then we just perform a copy of the snapshot when creating a volume 
or a template from the snapshot. XenServer has a UUID for each SR and each VDI. 
You cannot mount two SRs or VDIs with the same UUID at the same time. If you're 
interested, here's a video of mine demoing this feature:
   
   
https://www.youtube.com/watch?v=YQ3pBeL-WaA&index=13&list=PLqOXKM0Bt13DFnQnwUx8ZtJzoyDV0Uuye&t=1362s
   
   In any event, use case 2 allows you to temporarily use a SAN snapshot, but 
end up with a standard volume snapshot on secondary storage when all is said 
and done. It is this use case that is failing.
   
   I believe if you just look at the hypervisor type of the volume snapshot and 
pick any host in the applicable zone of the volume snapshot to perform the 
operation that all should be well.

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