[Freegis-list] Re: VMAP0/TIGER/SRTM30 data via BitTorrent

[Frank Warmerdam]

On Apr 3, 2005 1:20 PM, Sean Fulton <fulton at cmu.edu> wrote:
> This is very cool, by the way. However, the problem with Bittorrent is
> that it only to work well with popular files, i.e. files that with a lot
> of downloaders. I tried downloading the vmap0 data via those torrents
> and it was taking an excrutiatingly long time. I gave up and downloaded
> directly from NIMA.
> 
> Perhaps you could get a couple other sites to help seed(is that the
> right word?) the torrents?

Sean,

There are 3 seeds for the VMAP0 data, 2 for the tiger data, and
4 for the SRTM30+.  I doubt the problem is a lack of seeding.
However, there are definately performance aspects of BitTorrent
that I don't understand.  I have been getting terrible performance
via bittorrent at home since I switched to Cable instead of DSL.
But occationally it will pick right up to full speed, then it drops 
back to approximately 1KB/s. 

My geodatatorrents bittorrent server is limited to 100KB/s but
given the light loading and the other seeds, someone with
a good bittorrent client configuration should be able to pull stuff
down at 200-300 KB/s. 

However, your point about BitTorrent working best for popular
files is certainly true.  Downloads from of the torrents have
generally been just a matter of the seeds dumping to the 
"leeches" with very little peer-to-peer data sharing because we
so seldom have more than one or two leeches pulling data at a
time. 

All in all, the "geodatatorrent" experiment has been educational
but not terrible successful at distributing data efficiently.  I think it
might be more useful for big *new* datasets that might attract
alot of downloaders at the same time. 

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent