The Sans Digital TowerRAID TR4M-B  Enclosure is a Direct-Attached Storage (DAS) unit.  A DAS unit refers to a device that is directly attached to a server or workstation, without a network in between. The TowerRAID TR4M-B is a compact RAID tower utilizing the latest SATA II port feature, where one single eSATA cable connects to four 3Gpps SATA II hard drives. Designed with easy installation in mind, the trayless TR4M-B allows instant installation by simply inserting the hard drives after opening the protective ventilating cover. It supports JBOD and Spanning modes for instant storage expansion. It also supports RAID 0, 1 0+1, 5, 5+spare via included software utility, for high performance and hard drive redundancy. The package includes a 2-port eSATA PCIe card at no additional cost, which allows the connection between two TR4M units (up to 8 hard drives) using only two cables. PCI/PCI-X options are also available.

The TR4M-B can be configured anywhere from the base unit without drives all the way up to (4) 1TB drives. One can spend anywhere from $295 to over $1200 for a fully loaded unit with the optional 4-port PCIe card.  I took a quick look at Newegg to see what the street price of the base unit might be: approximately $225 shipped.  That is a very nice price for what you get: a 4 HD enclosure, power supply, JBOD to RAID 5 capability, port replication, hotswap capability, and a PCIe eSATA adapter.  The chart below provides you with the list price breakdown for the various versions.

Full Article