How to prohibit span over two HDDs?

[cwhitmore]

I think I already know the answer to this, but want to confirm. I'd like to setup one Protection Group that backups up two different Virtual Machines each night Thursday - Saturday.
I'd like each night to backup to one external HDD (Thursday-HDD, Friday-HDD, etc...). Since a protection group can only backup to one library I'm assuming that I will have to put all of the external HDD in one library. Will there be an issue with one night's backup spanning over two HDDs?
What's the best way to do this?

[jsf]

My understanding is that you have M+N tapes loaded into a library, M tapes on HDD1 and N tapes on HDD2. It's up to DPM to choose tapes, and all tapes look the same to it. For a particular backup, DPM may choose any tape(s) it likes, so it can choose (a) one or more tapes from HDD1 only; (b) one or more tapes from HDD2 only; or (c) one or more tapes from HDD1 and one or more tapes from HDD2. Firestreamer doesn't care; there should be no problem in any case.