[tahoe-dev] uploading unhappiness error messages

Greg Troxel gdt at ir.bbn.com
Wed Jan 5 14:04:35 UTC 2011


Brian Warner <warner at lothar.com> writes:

> On 1/4/11 9:36 AM, Greg Troxel wrote:
>> 
>> [show full servers on status page]
>
> Oh, that's an awesome idea. I'll add that to the accounting
> server-status page that I'm building for #666 now.

Thanks.  If that makes it into 1.8.2 I think it would vastly help
the n00b pubgrid experience.

>> From 1/1/10 to 1/3/10 just by changing configs, without any reencoding.
>
> I prefer k=3 H=1 N=10. That gets you good diversity if you have enough
> servers, good redundancy, and works successfully for any number of
> servers.

I see your point that this works on one server and has a good migration
path; I withdraw my 1/10 suggestion.

> I'm quite proud of the fact that tahoe will tolerate putting
> multiple shares on a single server, to provide this sort of flexibility
> to multiple use cases. (I'm less proud of the fact that it might do this
> when you don't expect it to, especially in the "I'm only talking to
> myself" case, but I think we're getting a handle on that).

Agreed - which makes we want the H=1 to be only on create-node --demo,
so a default node gets reasonable behavior for the real world.  I know
I've said this several times, but I believe it's critical for the
default behavior of a program that advertises redundancy to deliver that
redundancy (or fail).

> If you know that you'll always have at least X servers, then you can set
> H to something higher to force a failure when your expectations are
> violated (maybe set H equal to X, but I believe the happiness
> calculation is weirder than that).

I've been right on the edge with the pubgrid all the time, and so far it
has seemed like the calculations have been entirely reasonable and the
only issue lack of working servers with space for shares.

I changed from 3/7/10 to 2/5/7, but I suppose I could have gone to
3/5/10.  With 3/5/10 one might need 3 out of those 5, and that didn't
seem comfortable.  But really you only need 2 working servers, because
3/5/10 and 5 servers results in 2 shares/server, and I only just now
really figured that out.
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