Storage monster does it over Ethernet
Ditches IP, iSCSI and Fibre Channel for new protocol.
By Chris Mellor | Techworld | Published: 08:46, 23 February 2007
Coraid has introduced a free-standing tower of shared Ethernet storage, using a low-level protocol that avoids the need for Fibre Channel or iSCSI.
The EtherDrive SR1521T can hold up to 11.25TB of serial ATA disk capacity and communicates by Application over Ethernet (AoE), which is low level, much simpler than TCP/IP, and that does away with the need for Fibre Channel or iSCSI hardware.
TCP/IP and IP are necessary for the reliable transmission of data over the Internet, but for local area storage they aren't necessary, and introduce complexity that makes the the computer work harder, says Coraid. TCP/IP is a wide area network protocol designed for unreliable networks, while server access to local drives is a local network problem, the company said.
The ATA over Ethernet protocol takes advantage of today's smart Ethernet switches with their flow control which increases throughput and limits packet collisions. Packet order is preserved, and each packet is checksummed for integrity by the switch hardware.
Each AoE packet carries a command for an ATA drive or the response from the ATA drive. The O/S AoE driver makes the remote disks available as normal block devices, such as /dev/etherd/e0.0 (in Linux) just as the IDE driver makes the local drive at the end of your IDE cable available as /dev/hda. The driver retransmits packets when necessary, so the AoE devices look like any other disks to the rest of the kernel.
In addition to ATA commands, AoE can identify available AoE devices using query config packets. AoE is non-routing and limits access through ad hoc Ethernet networks. AoE is native in the Linux 2.6 kernel and software drivers are available for Mac OS X, Windows, Solaris, and FreeBSD. The technology comes from the Linux world which helps to explain why it is little known in the Windows and mainstream UNIX markets.
Customers can buy 3.5-inch disks of their choice to fill the 15 slots. These drives are hot-swappable. The SR1521T is geared at workgroups and departments that don't have access to datacentre racks for their shared storage needs.
"As your needs grow, you simply add more SR1521T's to the network using standard Ethernet," said Coraid CEO Jim Kemp. "The introduction of the SR1521T allows us to accommodate users that want the convenience and flexibility of low cost desktop storage."