Re: Aspera SCP software

[Ed Wilts <ewilts ewilts org>]

On Mon, May 16, 2005 at 04:24:26PM +0100, Ben wrote:
> On Mon, 16 May 2005, Ed Wilts wrote:
> 
> >We're currently looking at the Aspera SCP software for intercontinental 
> >file transfers.  Our initial tests have been successful (and much faster 
> >than FTP) but I'd like to know if anybody else is running it and what the 
> >opinions of both the company and product are.
> 
> So far the only thing I can see that Aspera SCP does that OpenSSH's scp 
> doesn't is cost money.

Actually, it does a bit more than that...  One of the things that it
does nicely is allow us to throttle the connections.  We've got enough
bandwidth to easily saturate our partner's bandwidth and they want to
limit the amount of data that we're pushing.  Aspera SCP takes that into
account.

> "The same application sustains 1 Mbps file transfers over T1 links, and 
> 200-300 Mbps transfers over high-speed dedicated circuits, independent of 
> network conditions."
> 
> I asked some people who know a bit more about TCP than I do about this 
> page:
> 
>  http://www.asperasoft.com/technology-fasp.html
> 
> and it seems it contains some blatantly false statements about TCP:
> 
>  "When TCP's rate is self-limited on an uncongested link, FASP detects the
>  unclaimed bandwidth and ramps up to fill it".
> 
> This sounds like someone who thought that congestion collapse doesn't apply 
> to them.  Personally it all sounds a bit dubious to be and I can't see why 
> you wouldn't use OpenSSH.

It does work well in practise.  The wide-area SAN people use the same
concept.  What appears to happen is that the transfers may go over UDP
instead of TCP so that you're not trying to ack every packet half-way
around the globe but can ack them in bunches.  The end result appears to
be a more consistent data flow.  

It's been one of my co-workers who has been doing most of the work so
far, and he's a fairly bright puppy so I don't think the Aspera software
is all smoke and mirrors.

-- 
Ed Wilts, RHCE
Mounds View, MN, USA
mailto:ewilts ewilts org
Member #1, Red Hat Community Ambassador Program