ATA over Ethernet

ATA over Ethernet ( AoE ) is a protocol developed by Brantley Coile network protocol for accessing storage devices (usually disks) via an Ethernet computer network. It uses the ATA protocol.

ATA over Ethernet transmits data in the form of Ethernet frames, and to dispense with the use of higher standing protocols such as IP, UDP or TCP. The transmitted by AoE Ethernet frames can not leave, so the use of AoE mainly on local storage area networks (Storage Area Networks) is limited the local network segment. AoE is technically simpler than iSCSI, which is true also transported over the network, but on higher layers.

So the biggest difference of AoE iSCSI is visible: AoE is only local ( switched) available, iSCSI, however, can generally be routed to other networks, although this possibility is rarely used in practice. By not using a complex infrastructure AoE achieved a speed advantage over comparable techniques.

AOE without the commands of the ATA protocol, which is used for communication between a computer system and a storage device connected thereto, is directly transmitted through a cable. However AoE packs these commands into data packets that it sends over an Ethernet network to another computer. This target system manages the ATA commands then through a driver to a block storage device (usually a hard disk) and return the reply packets once again using the network back. So is a very hardware-related access to a disk can also be over relatively long distances.

Through this technique, several systems can simultaneously access the same block storage device. The coordination of the write and read operations between the participating systems is carried out by a so-called " configuration string " on the managed server. The simultaneous access of multiple systems on the same device requires the use of special cluster file systems, because the popular file systems have not been designed for this application.

AoE is supported natively on Linux, OpenBSD, and VMware ESXi. For other common operating systems and hypervisor drivers from software vendors are available. In addition, there are special AoE host bus adapter, which take over the processing of the AoE protocol in the system, thus relieving the main processor.

Packet format

Operating systems with ATA over Ethernet support

Other protocols for addressing block devices

  • Fibre Channel: FC defines a non- routable protocol standard in the field of storage networks, designed as the successor to SCSI for high-speed transmission of large amounts of data. FC is not compatible with the Ethernet, it is a separate infrastructure (NICs, switches, etc. ) is required.
  • Fibre Channel over Ethernet: For Fibre Channel over Ethernet " Fibre Channel" packets are encapsulated in Ethernet. In contrast to iSCSI but there is no encapsulation in TCP / IP, this gave rise to low performance advantages, but FCoE is not routable.
  • Fibre Channel over IP over Fibre Channel IP " Fibre Channel" packages will be encapsulated in TCP / IP. FCoIP is therefore routable.
  • ISCSI ( SCSI over IP): With iSCSI, SCSI packets are encapsulated in TCP / IP. Unlike ATA over Ethernet iSCSI is routable.
  • HyperSCSI In HyperSCSI SCSI packets are encapsulated in Ethernet. In contrast to iSCSI but there is no encapsulation in TCP / IP, this gave rise to low performance advantages HyperSCSI is like AoE is not routable.
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