We use it to back up
Exchange 2k7
2 * SQL Servers (SQL 2000 [note it must be patched to SP4] AND SQL 2005)
1 * IIS Server
1 * WSS
4 others backing up part of the file system.
In so far as the actual back up is concerned - it does a full synchronization, then incremental. It effectively maintains a shadow copy of your data, and the space you need depends on how many restore points you are going to keep on disk. THe incremental backups are clever and I've seen a good article on how it works exactly - but rest assured, the data transfer is kept to an absolute minimum.
It works around protection groups. For example, We have a "userspace protection group", which covers two servers. DPM backs up the file system on each server.
For each file server you wish to backup in that protection group, you require a replica volume and recovery point volume.
The replica volume will be the total size of the data being backed up (plus a little more) - for us, we set this to the size of the disk we are backing up as we are in a fortunate position of having plenty of filespace on the backup server.
The recovery point volume effectively stores the changes between your replica volume and your recovery points. Therefore it's size will depend on a) the number of recovery points you use and b) the rate of change of data that you are backing up. To give you an idea, we have a file server with 430gb of space, 373 used so far. The replica volume is 430gb and the recovery point has 15gb allocated. We use about 6.05 of this, so there would be scope for making it smaller if we so wished (note you can only downsize when DPM is on server 2008). These are light users. In addition, we have another file server with heavier usage, which has 385gb/227gb on the replica and 30gb/23gb on the recovery point volume.
Our mail server has 70gb allocated, 59 used for replica and 20/3.54 on the recovery point for our main storage group. This covers about 5000 users, 4000 of which would be 'very light' users, the remainder being made up of medium to heavy users.
Like I said, we are well catered for in terms of storage and have a lot of capacity for expansion. Depending on your company circumstances you may need to plan a little more carefully than we did!
I'd be happy to answer any further questions if you wish.
