[tahoe-dev] Reliability Calculator fails on long time periods?

[jason.johnson at p7n.net]

I really need to find a easy way to update to 1.10 apt-get would be nice.

 

From: tahoe-dev-bounces at tahoe-lafs.org
[mailto:tahoe-dev-bounces at tahoe-lafs.org] On Behalf Of Garonda Rodian
Sent: Saturday, October 5, 2013 7:26 PM
To: tahoe-dev at tahoe-lafs.org
Subject: [tahoe-dev] Reliability Calculator fails on long time periods?

 

Looking at the Reliability Calculator on Jason Johnson's setup (1.9.2), and
then taking all defaults except for the last one (report_span), which I set
to 25Y from the default 5Y, I noticed that the probability of failure
without maintenance peaks at 15 years and 7 months at about 0.628, and then
starts decreasing again, which seems extremely odd.

Then changing drive lifetime to 7Y from 8Y, the peak changes to 13 years 6
months, also just over 0.628.

Then changing N to 15, the peak changes to 16 years 3 months, at 0.615

Then changing k to 4, the peak changes to 14 years 4 months, at 0.760

Going back to the defaults, except for changing k to 4, gives us a peak of
13 years 2 months, at 0.777.

Hopefully this will help track down the issue with the math (assuming it
wasn't fixed in 1.10.0 - I'm still working through python basics to be able
to quickly build test grids).

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