by Michel Machado - michel at digirati dot com dot br
Brookline, December 20th, 2005
The Serial ATA (SATA) electrical interface, which is gradually replacing Parallel ATA (PATA) on new hard drives (HDs), is a major improvement to the communication channel between disk and host device (desktop, server, or appliance). This improvement is so substantial that the SCSI group has been working on the Serial Attached SCSI (SAS) interface to try to catch up with SATA's success. Even though the serial strategy appears to be the right choice, the industry may be on the wrong path. With a different approach, instead of just another serial interface, the world could benefit from ATA and SCSI over Ethernet (XoE). Ethernet is serial, stable, standardized, well-known, and cheaper than Serial ATA.
Use of XoE would drastically reduce development and deployment costs. There would be no need to develop new electrical interfaces to disk drives. Ethernet offers multiple speeds, among them 10Mbs, 100Mbs, 1Gbs, and in the future 10Gbs (there already are 10Gbs chips on the market). End users could choose the speed they wanted based on their budgets and requirements. Moreover, Ethernet cables are cheaper than SATA or SAS ones, mechanically more robust, and allow as much air flow as SATA or SAS ones. In addition, they can be bought everywhere, or else easily made up by anyone.
XoE provides much more "bang for the buck" than SATA or SAS. Commercially available Ethernet standard switches allow everyone to use XoE-enabled HDs as the cheapest storage solution. As a bonus, XoE natively supports hot-swapping, since Ethernet is a hot-swap interface. End users would connect a XoE-enabled HD to their desktop or notebook just by using an AC adapter and an Ethernet card, which are widely available and affordable; No extra hardware is needed.
XoE is not a dream. The Linux kernel already included ATA over Ethernet (AoE) in its version 2.6.14. Coraid, the startup that created AoE, has sold AoE-based solutions to large users such as NASA, the FBI, and MIT. Others can quickly implement AoE in their products because the AoE specification is open, and small (only eight pages in length). HyperSCSI, a SCSI over Ethernet implementation, is older than AoE, but the SCSI over Ethernet approach has not received much attention.
XoE is still in its childhood, and aspects such as wireless connection have not yet been explored. Once wireless XoE were enabled, not only would XoE allow end users to connect HDs using wireless links, but it would also allow digital cameras, MP3 players, and cell phones to take advantage of this scenario.
XoE is more than just a way to connect disks to host devices; It leverages the network industry by providing it with a new market. Widespread adoption of this technology would bring faster and cheaper networks for everyone in a couple of years. The Ethernet standard won the fight against other network solutions to connect computers. Now, it is time for Ethernet to save the day again, and give us a better way to connect our disks.