For anyone struggling to get disks available in Microsoft DPM 2010.
I'd been trying to get DPM to use a free disk but everytime I went to use it it would say that there was no unallocated space.
I'd add the disk to DPM and it would show unallocated disk 0kb. Didn't seem to matter how I created the disk it would always say 0kb unallocated.
My mistake was that I was formatting the drives. If I just initialised the disk it would work. Also you could create a volume, but NOT format it.
Once I'd done that DPM shows my disks with 100% unallocated and hey presto I'm up and running.
This is probably blindingly obvious but when looking for 2010 documentation or deployment guides they either didn't seem to exist or weren't any use.