c|net cover AoE

c|net have just revisited AoE. ATA over Ethernet is a new(ish) technology developed by a startup called Coraid targeting iSCSI at the lower end of the network connected storage market. Fibre attached storage used to be the only game in town. Each server has dedicated fibre cards to connect to your storage hardware, either directly or through (expensive!) fibre switches. At work we have a *lot* of this kit, and it didn’t come cheap!

iSCSI is significantly cheaper because, in theory, you can use the same LAN to connect to your storage as you connect to the outside world. Basically standard SCSI data packets are wrapped in a TCP/IP wrapper and transmitted between hardware. Everything has an IP address, and it can even be routed over the internet. In practice however the CPU hit involved in achieving fast data transfer when every piece of data has to be processed by the CPU twice in each direction (once to wrap the data in a SCSI packet and once to wrap the SCSI packet in a TCP packet) means that the server isn’t much use for anything else. Thankfully you can get network cards that will do the process in hardware, but they’re even dearer than the fibre cards, so iSCSI isn’t a cheep option either.

AoE dispenses with the TCP layer altogether. It’s a very lightweight protocol that just uses the Ethernet network switch for routing, so you can use your server’s existing LAN hardware. Coraid have taken the decision to create a very low entry cost. It uses generic SATA disks, so all you need to buy from them is the AoE enclosure, which starts at < ???????4K for a chassis that'll take 15 disks. If it doesn't work out, you can re-use the disks elsewhere and just bin the enclosure. 750GB disks are ???????400 each, so I could deploy a 10TB array for < ???????1/GB.

I sincerely hope these guys succeed. Right now Coraid are the only manufacturer of this kit, and even though they're selling a lot of hardware to universities and research organisations (NASA are a customer), the iSCSI vendors are probably not happy with an upstart eating at their table, and may decide to kill them off, leaving customers in the lurch...

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