This behavior might confuse a novice but it is possible.

Assume that an appendable tape is used in one drive for recoveries. Trying to 
serve you best, NW will just use another appendable tape from the same pool. 

Also keep in mind that  for a partial written (aborted) clone job NW would need 
another tape with the next attempt as the SSID is already assigned and it must 
not repeat on the same media. 

Just to mention 2 conditions for the same pool. 
If you have more pools and you use them all, NW will require at least need one 
tape for each pool.

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