ATA over Ethernet
ATA over Ethernet ( AoE ) is a network protocol developed by Brantley Coile for access to storage devices (usually hard drives) via an Ethernet computer network. It uses the ATA protocol for this.
ATA over Ethernet transmits the data in the form of Ethernet frames and does not use higher-level protocols such as IP , UDP or TCP . The Ethernet frames transmitted by AoE can not leave the local network segment , which is why the use of AoE is mainly limited to local storage area networks . AoE is technically simpler than iSCSI , which is also transported over the network, but over higher layers.
This shows the biggest difference between AoE and iSCSI: AoE can only be used locally (switched), iSCSI, on the other hand, can basically be routed to other networks, although this option is rarely used in practice. By doing without a complex infrastructure, AoE achieves a speed advantage over comparable technologies.
Without AoE, the commands of the ATA protocol, which is used for communication between a computer system and a storage device connected to it, are transmitted directly via a cable. However, AoE wraps these commands into data packets that it sends to another computer over an Ethernet network. This target system then forwards the ATA commands via a driver to a block storage device (usually a hard disk ) and also returns the response packets via the network. This means that access to a data carrier close to the hardware is possible even over a relatively long distance.
This technique allows multiple systems to access the same block storage device at the same time. The coordination of the write and read operations between the systems involved is carried out by a so-called "configuration string" on the managing server. The simultaneous access of several systems to the same device requires the use of special cluster file systems , since the common file systems have not been designed for this application.
AoE is natively supported on Linux . Drivers for other common operating systems and hypervisors are or were available from software providers. There are also special AoE host bus adapters which process the AoE protocol in the system and thus relieve the main processor.
Packet format
| Offset | Data type | description |
|---|---|---|
| 0 | char [6] | Destination address (MAC address) |
| 6th | char [6] | Return address |
| 12 | uint16_t | Ethertype: 88A2 hex |
| 14th | uint8_t | Version (bit 4… 7), currently always 1; Flags (bit 0 ... 3) |
| 15th | uint8_t | Error |
| 16 | uint16_t | Major address |
| 18th | uint8_t | Minor address |
| 19th | uint8_t | Command field |
| 20th | uint32_t | Command mark (day) |
| 24 | struct arg_field | Arguments including transmitted data from the hard disk |
Operating systems with ATA over Ethernet support
| operating system | Support | Third-party driver |
|---|---|---|
| Linux | Native (2.6.11 and higher) | Coraid |
| Mac OS X 10.4 and higher | Third party | 2DegreesFrost |
| Mac OS X 10.5 and 10.6 | Third party | Small Tree Communications |
| Solaris | Third party | Coraid |
| FreeBSD | Third party | Coraid |
| OpenBSD | Native (4.5 to 5.7) | |
| VMWare | Third party | Coraid |
| Plan 9 from Bell Labs | Native |
Other protocols for addressing block devices
- Fiber Channel : FC defines a non-routable standard protocol from the field of storagenetworks, which was designed as the successor to SCSI for the high-speed transmission of large amounts of data. FC is not compatible with Ethernet, a separate infrastructure (NICs, switches, etc.) is required.
- Fiber Channel over Ethernet : With Fiber Channel over Ethernet, “Fiber Channel” packets are encapsulated in Ethernet. In contrast to iSCSI, however, there is no encapsulation in TCP / IP, which results in minor performance advantages, but FCoE cannot be routed.
- Fiber Channel over IP With Fiber Channel over IP, “Fiber Channel” packets are also encapsulated in TCP / IP. FCoIP is therefore routable.
- iSCSI (SCSI over IP): With iSCSI, SCSI packets are encapsulated in TCP / IP. In contrast to ATA over Ethernet , iSCSI can be routed.
- HyperSCSI With HyperSCSI, SCSI packets are encapsulated in Ethernet. In contrast to iSCSI, however, there is no encapsulation in TCP / IP, which results in minor performance advantages, HyperSCSI, like AoE, cannot be routed.
Web links
- Items:
- ATA Over Ethernet: Putting Hard Drives on the LAN - Linux Journal (April 28, 2005)
- ATA-over-Ethernet enables low-cost Linux-oriented SAN. Archived from the original on October 13, 2007 ; Retrieved December 8, 2012 . - LinuxDevices.com (June 23, 2004)
- Protocol:
- Emulator and tools:
- Project overview for ATA Over Ethernet Tools and vblade at SourceForge - vblade is the server-based part of AoE and runs in user space
- vblade, implemented as a kernel module, is faster than the userspace implementation
-
qaoed - Mulithreaded ATA over Ethernet storage target runs in user
space
- qaoed - new location on Google Code
-
Aoeserver - Mulithreaded ATA over Ethernet storage target implemented as a kernel module
- aoeserver - spin-off / further development at Google Code
-
ggaoed - latest implementation with specialization in line properties for speed optimization
- It utilizes Linux kernel AIO, memory mapped sockets and other Linux features to provide the best performance.
Individual evidence
- ↑ Archived copy ( memento of the original from October 25, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ AoE (ATA over Ethernet) ( Memento from December 27, 2012 in the Internet Archive )
- ↑ Linux Support for AoE EtherDrive (R) Storage ( Memento of the original from May 16, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ 2DegreesFrost: AoE driver for OS X
- ↑ Small Tree - The Mac Network Experts: AoE driver for OS X
- ↑ Coraid AoE Solaris Support ( Memento of the original from June 18, 2010 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ FreeBSD AoE Support ( Memento of the original from June 24th 2010 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ VMWare CORAID AoE Support - EtherDrive ESX HBA Driver ( Memento of the original from June 22, 2010 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Plan 9 from Bell Labs ( Memento of the original from April 28, 2006 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
