Kernel Korner - ATA Over Ethernet: Putting Hard Drives on the LAN
Because ATA over Ethernet puts inexpensive hard drives on the Ethernet network, some sysadmins might be interested in using AoE in a backup plan. Often, backup strategies involve tier-two storage—storage that is not quite as fast as on-line storage but also is not as inaccessible as tape. ATA over Ethernet makes it easy to use cheap ATA drives as tier-two storage.
But with hard disks being so inexpensive and seeing that we have stable software RAID, why not use the hard disks as a backup medium? Unlike tape, this backup medium supports instant access to any archived file.
Several new backup software products are taking advantage of filesystem features for backups. By using hard links, they can perform multiple full backups with the efficiency of incremental backups. Check out the Backup PC and rsync backups links in the on-line Resources for more information.
Putting inexpensive disks on the local network is one of those ideas that make you think, “Why hasn't someone done this before?” Only with a simple network protocol, however, is it practical to decouple storage from servers without expensive hardware, and only on a local Ethernet network can a simple network protocol work. On a single Ethernet we don't need the complexity and overhead of a full-fledged Internet protocol such as TCP/IP.
If you're using storage on the local network and if configuring access by creating Ethernet networks is sufficient, then ATA over Ethernet is all you need. If you need features such as encryption, routability and user-based access in the storage protocol, iSCSI also may be of interest.
With ATA over Ethernet, we have a simple alternative that has been conspicuously absent from Linux storage options until now. With simplicity comes possibilities. AoE can be a building block in any storage solution, so let your imagination go, and send me your success stories.
I owe many thanks to Peter Anderson, Brantley Coile and Al Dixon for their helpful feedback. Additional thanks go to Brantley and to Sam Hopkins for developing such a great storage protocol.
Resources for this article: /article/8201.
Ed L. Cashin has wandered through several academic and professional Linux roles since 1997, including Web application developer, system administrator and kernel hacker. He now works at Coraid, where ATA over Ethernet was designed, and he can be reached at firstname.lastname@example.org. He enjoys music and likes to listen to audio books on his way to martial arts classes.
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