Hello,
You should be able to use both, however, consider the consiquinces.
1. What might be the panalties when Disk staging is being performed.
2. Will it meet your backup window.
3. Are your client backing up slow over the network and will benifit from 
backing up to disk or you will gain very little ?
4.What is your primary perpose to backup to disk, is it slow network 
attached client\small files or is it ablility to retain data for instant 
restore ?
5.Could backup to disk be any faster then backup to tape in your case ?
6. Create no more then one device per one disk partition for best 
performance.
Do some testing with and without and you will have the answer.

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