+1, total overkill for 4TB but.....
the Hitachi AMS system is not the cheapest but it is probably the best out of the lot for block-level, it just pips the Netapp 3070 in terms of performance and reliability.
I am a big fan of the Netapp approach but it's OS is a little too buggy and requires constant maintenance.
The 450GB 15k SAS disk performance in the AMS is excellent, in a 8D+1D RAID group it will give you 1900 IOPS.
The dynamic pool system means that if any of the RAID5's fail, one of the array level hot-spare's is slotted in automatically, a bit like WAFL.
It is disappointing that the disk-tray's on the AMS are 3U however, this is offset by the flexibility of being able to use up to 3 of your own racks if you want to spread things out.
The high-density trays are now available but I am not sold on the them, they are not supported in all datacentres due to the weight and heat problems. They can only be used in a limited fashion and racked at the base of the rack only.
The IBRIX systems run with these trays and they cause heat management problems.