It has been a while since I last discussed Coraid, but two announcements the company made at LinuxWorld earlier this month have me thinking about AoE (ATA over Ethernet) these days.
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To refresh your memory, AoE is an open source, reliable SAN transport protocol that uses MAC addresses to connect servers to their storage.
One of the knocks against AoE is that it is not routable. You can have as many arrays and disk drives as needed, but those machines and their application servers must live within broadcast reach. If this limitation is unacceptable for your requirements, you can use IP tunneling or other tools to cross those boundaries, or you can move to another protocol such as FC or iSCSI.
Another significant delimiter: AoE doesn’t support SCSI or FC drives, which means that to compensate for the SATA performance gap you must use more drives. Even so, at a cost of around $0.70 or less per gigabyte, according to Coraid, you could still get the same performance and come out ahead.
Deploying AoE in a recent version of Linux should be a breeze. According to Coraid, the kernel, from 2.6.11 on, already includes the proper drivers. Moreover, your distro, like this Ubuntu 7.04, should include the tools to discover and manage AoE storage arrays.
If your server farm includes more than just Linux machines, AoE now has drivers for Mac OS X, Windows, and Solaris, but you may have to pay a licensing fee for the first two. By installing Vblade, however, a Linux application that emulates an AoE target, you can kick the tires of AoE storage for free.
Chief among the numerous novelties Coraid CEO James Kemp mentioned in a recent conversation about AoE is an open source driver for Windows, which was developed as part of the EtherBoot Project and should become available shortly. Also worth noting is that Taiwan-based Welland has deployed the protocol in its own chips, which it will use in a SAN box for SMBs.