[tahoe-dev] using the volunteer grid (dogfood tasting report, continued)

Shawn Willden shawn-tahoe at willden.org
Wed Apr 8 23:16:18 UTC 2009


On Wednesday 08 April 2009 04:04:34 pm zooko wrote:
> Then I had an idea.  There are currently 13 servers registered with
> the volunteer grid introducer.  (Okay, so only 10 are currently
> connected to the introducer, and that includes my own localhost.)
> Why not upload the same file with K=13 and see if it downloads
> faster?  I set shares.needed to 13 and shares.total to 16 in my
> tahoe.cfg, restarted the node, and re-uploaded the file.  Now when I
> wget it, it comes down at around 150 KB/sec!  Whoo!  Now I can stream
> it!

This is a big part of the reason why I think the loss modeling work is 
important.  In order to get good performance, you want n to be large.  On a 
stable grid of small to moderate size, you probably want to set m equal to 
the number of available servers, then adjust n to trade reliability off 
against performance and expansion.  Higher values of n provide better 
performance (up *and* down) and less expansion but worse reliability.

This means that it's tempting to set n close to m.  But if you do that, just 
how bad *is* your reliability?  I want to be able to provide users a simple 
way to make this tradeoff, presenting them with a list of reliability and 
performance estimates and letting them choose the one they feel is most 
appropriate.

	Shawn.



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