The SAT3540U3ER 4-Drive USB 3.0/eSATA to 3.5-Inch SATA RAID Enclosure is a high-performance external RAID storage solution that supports up to 4 high capacity (tested with up to 4TB per bay) 3.5-inch SATA hard drives over a USB 3.0 or eSATA connection. The 4-bay RAID enclosure can be connected to the host/source computer through USB or eSATA and automatically builds your SATA RAID array based on your selection (Spanning, RAID 0, RAID 1, RAID 1+0, RAID 3, and RAID 5 supported), delivering a simple, yet flexible external storage solution. Designed for convenience, the enclosure features front panel LED indicators that provide RAID information and simple hard drive status and activity monitoring. The enclosure also features a built-in, 3-speed 80mm fan with automatic or manual controls that enable you to customize the speed of the fan as necessary to ensure suitable operating temperatures for optimized drive performance.