The newest versions of the Storage Calculators for DPM 2010 were republished and they confirm what has plagued me for years when trying to backup Hyper-V VMs to disk. If you look at the screenshot below from the DPM 2010 calculator for Hyper-V you will see that for the 3 host example there is 465GB of VMs.
As you scan down however you see that in order to keep a 7 day retention (15% churn noted on another tab) on these VMs you will need a little greater than 1TB to back it up. 1TB is not that large these days, but the percentage of additional disk space over the source data is greater than 100%. In my environment I have over 20TB of VMs this would equate to 40TB+ of data for DPM disk based backups. That number gets a little expensive and is the reason why I do not use DPM disk based backups. Lets hope the deduplication feature in Windows Server 8 has some significant effect on storage space requirements in DPM 2012. If not, look for 3rd party Hyper-V backup vendors that already include a deduplication (i.e. Veeam, Altaro) to continue to gain customers.