by November 4, 2006 0 comments

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
An alternative way to build your storage area networks 
Primary Link:
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

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

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.

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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