The 4TB 2big Quadra USB 3.0 2-Bay RAID Array by LaCie is a dual bay RAID enclosure that features 2x 2TB hard drives, running at 7200 rpm with a 32MB cache. The external enclosure also features USB 3.0/2.0 and FireWire 800/400 connectivity, giving you the flexibility and options to attach this unit to older PCs and Macs.
USB 3.0 offers an interface transfer rate of up to 5.0 Gbps, while the average (sustained) transfer rate is 210 MBps. The FireWire transfer rate is 800 Mbps max, and the average transfer 82 MBps. It supports RAID 0 (both disks are counted as one large drive) and RAID 1 (striping the data for redundancy and backup) and is preconfigured as RAID 0. The drives are user-serviceable and hot swappable, meaning that you can replace them at any time with fresh drives for more storage capacity.
There are also a number of features that give the LaCie 4TB 2big Quadra an added layer of protection. Besides the redundancy of data in Raid 1 mode, the unit also ships with professional backup software for timed and scheduled backups that include file-level and system-level restores. This gives you the option of performing a full system backup that would let you boot your Mac directly from the 2big Quadra. It's compatible with Time Machine and Windows 7 backup, and there's even a Kensington lock slot to prevent physical theft of the unit.
Another feature that ensures reliability in your data protection is the effective dual cooling system. An overheated drive can mean the difference between restore and failure, and LaCie has implemented a system that consists of three components - a solid aluminum heat sink, a thermo-regulated magnetic levitation fan, and numerous large venting holes for air dissipation. The fan controls speed based on the ambient temperature of the unit, so it's energy efficient and quiet since it is not spinning unnecessarily all hours of the day. You can also set the unit to deliver email alerts when a temperature or RAID level is approaching a critical status to help you plan ahead and avoid crashes.