We have a number of medium size client sites that we support with an average of 150 users at each site.
Their file server data repository has now grown to just under 2T . We backup with SCDPM 2012 SP1 onto LTO5 1.5/3T standalone tape units.
DPM does not allow you to create a Protection Group with just the differential data from the last full backup onto tape.
We have the desired recovery point options when backing up disk to disk but not directly to tape – could you check if this can be configured somehow.
Backup windows now span well into business hours due to this and in some cases take more than 24hours to complete – The latter is due to backing up millions of files in our current email archive solution repository.
We obviously do not require a full daily backup of this data and the backup to disk options requires the client investing in addition hardware for each of it 20 sites which they see as not feasible.