Article View: comp.arch
Article #2151Re: Synchronizer failure; MTBF
From: Nirmal Saxena
Date: Thu, 07 Sep 1989 21:08
Date: Thu, 07 Sep 1989 21:08
35 lines
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1440 bytes
I am not sure if your analysis is entirely correct:
>>First, let's compute the probability that one or more of the 50,000
>>systems will fail sometime within 5 years due to a synchronizer failure:
>>
>> P = 50000 * [1 - exp(-5/100)]
>> P = 1
P should be:
P = 1 - [1 - exp(-5/100]^50000 which is approximately unity.
>>Let's see what happens if we let the probability of 100 or more
>>failures be 33 percent. (Thus we have a 1-in-3 chance of being fired by
>>the Big Boss because of >99 synchronization failures in the field).
>>
>>
>> P(100 or more failures
>> 0.33 = out of 50,000 units = (50,000 / 100) * [1 - exp(-5/m)]
>> over a 5 year period)
>>solving,
>> m = required MTBF of synchronizer = 7,573 years
The correct equation should be:
0.33 = (sum from i=100 to 50000) { C(50000,i)*[1-exp(-5/m)]^(50000-i)
*[exp(-5/m)]^i }
Then we have to solve for m.
Here C(50000,i) is 50000 choose i (binomial coefficient)
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Path: arc1-ca.pugleaf.net!utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!brutus.cs.uiuc.edu!apple!motcsd!hpda!hpcupt1!hpsal2!saxena From: saxena@hpsal2.HP.COM (Nirmal Saxena) Newsgroups: comp.arch Subject: Re: Synchronizer failure; MTBF Message-ID: <2280011@hpsal2.HP.COM> Date: 7 Sep 89 21:08:44 GMT References: <26811@obiwan.mips.COM> Organization: HP System Architecture Lab, Cupertino Lines: 35