ATA over Ethernet

Storage area networks are traditionally built using iSCSI or Fibre Channel because speed and reliability are key concerns. Now, regular ATA drives can be connected over Ethernet using a new protocol called AoE

Saturday, November 04, 2006

ATA over Ethernet (AoE) is a new protocol for building economical and less complicated SAN solutions. These solutions are suitable for organizations that have a heterogeneous OS environment and want a storage solution that is easier to maintain. Setting up iSCSI or Fibre Channel not only has a high cost factor attached, but also involves higher maintenance due to their complex architecture. Also involved is the cost of expensive drives, additional components and installation.

As there always has been a huge demand for low cost and flexible storage solutions, it is not feasible to increase the number of drives easily in either Fibre or iSCSI based SANs. The ATA over Ethernet (AoE) protocol solves this issue to a large extent. However Fibre channel solutions are the fastest of the three while iSCSI solutions are still most reliable. Both Fibre Channel and iSCSI are better suited for speed intensive scenarios compared to a similar AoE solution. Let us now understand the concept behind ATA over Ethernet and see how it is useful.

Applies To: Storage managers USP: An alternative way to build your storage area networks  Primary Link: www.coraid.com Google Keywords: Ethernet ATA

What is AoE?
ATA over Ethernet is an OpenSource protocol registered with IEEE, which provides access to inexpensive ATA drives over Ethernet for data storage applications. These AoE storage devices work exactly like normal hard drives, attached directly to a server. The AoE protocol is used to connect disks to the servers using Ethernet. In case of iSCSI requests like read and write instructions are processed over TCP/IP layers, whereas in AoE these are incorporated in the AoE Ethernet frame. This reduces complexity and delivers better performance than solutions utilizing higher layers for these requests. The AoE protocol is a block storage protocol similar to PATA and SATA.

Typically, in directly attached storage, any read-write request to ATA drive is first acknowledged by the ATA driver. The driver then sends this request to the drive over the ATA cable connecting the drive to the workstation. The OS considers these AoE drives as directly attached and treats the request similar to PATA or SATA drives. The AoE driver sends the requests over an Ethernet link to the AoE device.

AoE is a non-routable protocol. Hence, it doesn't require the TCP/IP layer for communication. The AoE initiator transmits a configuration string on the network periodically. AoE devices then revert back to these transmitted signals by AoE initiator with their presence information (ie, addresses for volume numbers). If any request for read or write is made for a drive, then AoE initiator sends frames with unique tags for disk like their row and stack column number to pin-point the particular drive. After the execution request, the AoE target disk sends an acknowledgement to the AoE initiator. The disks installed are denoted and accessed, based on their slot and shelf numbers.

Being a simple storage solution, it can be configured with any storage virtualization or volume management tools available. As these file systems do not require any proprietary network protocol, any file system like EXT3, JFS or XFS can be installed and used by workstations working on a heterogeneous platform.

It also supports cluster file systems like GFS and Lustre. These file system layers come directly over the AoE layer if there is no volume management system deployed.

The AoE data packets have MAC addresses for the source and destination but this is valid only for data that is being transmitted within the same network. The drives don't have an IP address so they can be added or replaced as required. You can use applications like storage management solutions for providing space allocation to different users and setting up RAID functionality.

Benefits
AoE can address a large amount of storage concerns for mail servers, file servers, Web servers and clusters. There is lesser protocol complexity in AoE protocol transmissions compared to iSCSI or Fibre Channel. The benefits of using an AoE solution are lower cost of data storage compared to other storage solutions, and a decrease in the hardware, installation and maintenance costs.

The drives are easily configurable for different RAID levels within the same device, for enhanced data reliability and performance.

AoE products support RAID level 1 to 5. Using an ATA drive has the additional benefit of flexibility. If at any point of time you need to change the drive, all you have to do is pull out the older drive and insert another one in its place. You can connect devices directly to any workstation or server and view its content. Such kind of flexibility is not available with other solutions.

Hardware and drivers
Initially, the AoE protocol was meant for Linux only, but now it is available for Windows, BSD, Mac and even Solaris. Mac drivers are available from '2 degree Frost Software' and for Windows from 'Rocket Division Software,' for a price.

The Solaris driver is still in beta. You can download trial versions of these drivers. AoE is still a relatively new protocol and none of the big players have solutions based around it yet. The only implementable solution available so far is from Coraid.

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