Let me answer your question as follows:
  - "Storage nodes" contains a failover list. So it may of course contain more 
than one SN name.
  - "Enablers are disablers". If you enter at least one name, you automatically 
exclude all others. If you want to 'enable' more, add them to the list.
  - The client can only backup one storage node at a time. As mentioned, this 
is a failover list. Consequently, it should have no impact on the speed. But 
this of course depend on your environment and the workload for this SN.
  - Of course you must ensure that all other pool criteria are met. Otherwise 
you will receive an appropriate "Waiting for media..." message.

Does this help?

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