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

[Sean Fulton]

Frank Warmerdam wrote:
> 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. 

Frank,

I may have spoken too soon. I tried the vmap0 data shortly before your 
original e-mail (heard about it through mapping hacks) and the download 
speed was incredibly slow. I just now tried the TIGER data and I'm 
getting it as fast as I can take it. It's actually showing 3 seeds.

> 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,

Agreed. Also, I think it can be useful as sort of distributed mirror of 
data which is how it's behaving for me now.

I think it's a worthwhile effort. I'd like to see the GLCF and other 
clearinghouses, especially those distributing raster data, do something 
with bittorrent.

	Sean