Personally, I would go with five 1TB drives with a RAID 5. You will have 4TBs. The other way on 2TBs. Then a hot spare. Or 2 X 2 TB in a mirror for 2TBs total with a hot spare. Sandeep will disagree on the first.
Disclaimer: RAID is at the hardware level and has nothing to do with a server. You don't need RAID for a server to work. These same considerations should be taken into account regardless if you choose Windows 7 or Small Business Server 2011 Standard with Premium Add-On.
That would give you a 3TB usable capacity not 4TB. With the 5 drives in RAID 5, you'll need an 8 Port RAID Card since they're made in increments of 4. $530 RAID Card + 5 x 1TB RE4 (5 x $120) = $1130 just for the drives and card. Probably better go with 3 drives in RAID 5 and a hot spare. You would get way way more speed with the SSD+HDD Hybrid.
You don't really need hot spares for RAID 1 and RAID 10. The rebuild time is much faster compared to a RAID 5 since there are heavy parity calculations involved in RAID 5. So I'd probably go with a 4 Drive RAID 10 with cold spare on a 4 port RAID controller ($330) or a RAID 1 with a cold spare. This is SBS Essentials which doesn't have very high requirements.
I think the best would be a double RAID 1. RAID 1 Crucial M4 + RAID 1 1 or 2TB Drives depending on need. I've only filled about 100GB of Data in the past 10 years at the office.
Pricing (According to a ~1TB Capacity):
1 TB Hard Drive = No RAID = $120 (Average, no speed boost or redundancy)
2 x 1TB RAID 1 = $200 RAID Card (2 Port Dedicated RAID Card) + $240 2 x 1TB Drives = $540 (Basic, bear in mind this is more than enough for Essentials)
4 x 500GB RAID 5 (w/Hot Spare) = $330 (4 Port Dedicated RAID Card) + $400 4 x 500GB = $730 (Fast, 1 TB Usable)
4 x 500GB RAID 10 = $330 RAID Card (4 Port Dedicated RAID Card) + $400 4 x 500GB = $730 (Very Fast, 1TB Usable)
128GB x RAID 1 + 1TB x RAID1 = $330 RAID Card (4 port Dedicated RAID Card) + $200 (RAID 1, Crucial M4) + $240 (RAID 1, 1TB WD RE4) = $770 (Insanely fast- you would need 10 hard drives to compete with these SSDs, 1.128GB Usable)
5 x 500GB RE4 RAID 5 (w/Hot Spare) = $530 RAID Card (8 port Dedicated RAID Card) + $500 5 x 500GB = $1130 (Very Fast, 1.5TB)
Obviously, adjust according to your storage needs. Personally I think 1TB is enough. We have yet to fill up 100GB so 1TB (1000GB) is more than enough.
My choice: I'd go with the basic RAID 1 (2 X 1TB) since it's Essentials. If not, the double RAID 1 with the 2 SSDs and 2 Hard Drives. I personally have the 4 Drive RAID 10 because when I bought my server. 128GB SSDs were $300-$400 each and 500GB Hard Drives were only $80. If I had this pricing now I would definitely get the SSD+HDD combo.
.png "ACUF Donor I")
