Re: AoE - ATA over Ethernet - comments?

Like any technology, AoE's suitability depends on what you want to do with 
it. The main points to consider are:

- AoE is a Layer-2 protocol. Its frames cannot be passed between LANs via 
a router, so AoE may not be suitable for mobility applications or off-site 
replication, etc.

- A directly attached IDE HDD has typical sustained read throughput of 
56MB/s. Translated to AoE and assuming an MTU of 1500, that same 
throughput will require 56k frames/s, consuming 47% of a gig-ethernet 
interface. The frame rate could pose a serious burden on the CPU, so AoE 
may not be suitable for applications having high throughput requirements. 
The use of jumbo ethernet frames would help this issue by reducing the 
frame rate and would also improve the performance of the IDE itself by 
delivering more data per ATA command. Regardless, a separate LAN should be 
dedicated to the AoE protocol if AoE traffic volume will be high.

- AoE frames are checksummed and retransmissions occur for unacknowledged 
requests. (Every request must be acknowledged.)

- AoE exports raw storage, so it supports any file system.

- AoE is a very simple protocol - perhaps much simpler than NBD - perhaps 
too simple for your needs?

... Dave






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12/07/2005 06:50 PM
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        Subject:        [ENBD] AoE - ATA over Ethernet - comments?


Hello !

sorry - I know this is slightly offtopic, but a little relation to ENBD is
probably given, though: 
ATA over Ethernet is a technology for sharing block devices via LAN.

Since there maybe many competent people on this list, I`d be interested, 
if
someone would like to give a comment (personal opinion) about AoE.

AoE is an open protocol and there is GPL'ed code:

- an AoE Client for Linux
- an AoE Server (2 variants: vblade [userspace] and vblade-kernel -
vblade-kernel has no project website for now, but it is working). I can
provide a link on request.

There is also a beta driver (closed source) for an AoE Client on windows. 


The best "entry" to AoE is the inventor`s website at www.coraid.com


I gave AoE a try and it works for me. 
It`s easy to understand, easy to install and it's fast, too.
>From my first point of view: great stuff, too! 

But - should I really trust AoE for now ?
Why is such more or less "trivial" technology born that late? what are the
caveats ?
Why should i use NBD/ENDB instead of AoE ? (ok, i cannot route AoE, but I
don`t need to route on my Lan/FakeSan add all)

Should ATA commands really be send over "unreliable" Ethernet at all ?
What happened to HyperSCSI? (similar concept, but seems completely dead
project)

Sorry for the noise - but maybe some of you find AoE interesting, too.

Regards
Roland

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