where i work we're on HP and you should be able to do this with Proliant servers. Get a DL 380 with 2-3 P812 RAID controllers. for the storage get a MSA 60 with the 2TB SATA drives. it holds 12 drives so it's 24TB raw storage, 22TB after RAID5 and i'm not sure how much after formatting. this is based on one RAID5 per MSA.

Each P812 has 2 external connectors and you can cascade something like 8 MSA's per connector

your big headache is going to be backup. for something like this you will need LTO-5 tapes or a D2D solution with a lot of storage. I would make sure that your DB server and backup servers are 10 gigabit and 6G SATA/SAS. A Proliant DL 380 G5 will be too slow due to it's older I/O channel

Check out the Proliant DL 380 G7. G8 will be out April to June of 2011.