[volunteergrid2-l] Problems

[David-Sarah Hopwood]

On 04/10/12 02:28, Shawn Willden wrote:
> I use it for my backups, but I also have constant struggles with upload availability.
> 
> I think part of the problem is that the configuration which I suggested to everyone here
> just doesn't work very well.  Allmydata.com always used 3-of-10 encoding, and it seems
> like everyone else other than those of us on VG2 are using that or something similar.  The
> math says that something like 10 of 15 is just as reliable and more efficient...

I don't follow the reasoning there. I think you might be assuming that all 15 chosen
servers for a file always accept shares.

> but the software just doesn't seem to work well when you do that.

Well, you're requiring that at least 10 servers operate correctly (if shares are evenly
distributed). That's very different from requiring that at least 3 servers operate
correctly. Loss of shares is not the only potential failure mode, especially for
availability problems (as opposed to preservation of successfully uploaded files).

> I'm considering trying a 3-of-10 setting.

VG2 seems to have exposed a particular problem that occurs for uploads and repairs
when the servers-of-happiness threshold is close to the number of servers accepting
shares. Unfortunately this isn't very easily reproducible, and so it isn't clear whether
this is due to some servers not accepting shares, or whether there is another bug in
the upload/repair code.

In any case, I recommend reducing both shares.needed and shares.happy. (Reducing just the
latter would reduce reliability.)

-- 
David-Sarah Hopwood ⚥

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