AoE has some real advantages over the other storage area network protocols in regards to scalability and performance. The biggest advantage with AoE lies in the fact that it is datagram based and not connection based. Fibre Channel and iSCSI are both based on a connection from the storage initiator and the target. This made sense when network technology was limited and a single 100 million bit per second network was all anyone could afford. At Fibre Channel prices you would only buy one host bus adapter for your server. In those days a single connection from the server through the single adapter through a single path in the switch fabric to a single port on the target was as fast as you could go.
But now times have changed. Ethernet technology has surpassed Fibre Channel in speeds, it now has 10 billion bits per second, and has made one billion bits per second an inexpensive commodity. Current price for a 1Gb switch is about $15 per port compared to a 4Gb Fibre Channel switch from about $800 per port. Host interfaces to Fibre Channel are about $1,600, with the cheapest off-brand still being as high as $1,000. For VMware ESX servers, a CORAID EtherDrive Host Bus Adapter costs only $99 and include two 1Gb ports.
This all makes using multiple links to the storage attractive. By putting more Ethernet ports on a server, which can easily be done with dual and quad port EtherDrive HBAs, storage traffic can use all the available links. This can't be done with storage protocols that are based on a connection between the server and the storage. Fibre Channel is a five layer protocol based on named ports in the storage and the switching fabric. A complicated scheme called multi-pathing is used to allow standby routes to the storage in the event of a failed link. The iSCSI protocol rides on top of TCP/IP, which provides a connection between two IP host ports. It also has a single path through the network to the host, meaning that it is limited to the speed of a single port on the initiating machine.
AoE, however, is a datagram based protocol. That means that each request and response packet that is not part of a connection and can use any port available to access the storage. If an initiating machine has four one billion bits per second ports requests are sent out each simultaneously making a couple of $99 HBA run as fast as a $1000+ Fibre Channel card. Fibre Channel and iSCSI can't do that, no matter how many HBAs you put in the initiating system.
For information on CORAID EtherDrive SAN visit www.coraid.com