Hello,
If the same Drive in question is speedy ( during normal backupa) your 
problem may be all 4 drives in use while staging or something else.
But u can rule out the drive it self having problem by the test above and 
ofcource check drivers etc.
Networker has BIGASM for testing and MT might be able to test as well.
Run a backup without going to disk and if the tapes writes well your 
problem is staging.

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