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Senerjp
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Iron
Re: Definitely a trend to watch
Senerjp   10/4/2011 10:18:46 AM
NO RATINGS
Two controllers, if they are truly ustilizing multi-pathing, would actually act in parallel and would be more reliable. R = 1-(1-R)^n so to the extent they are completely seperate ( which nothing ever truly is) they would approximate R=.9999!

Ivan Kirkpatrick
User Rank
Platinum
Definitely a trend to watch
Ivan Kirkpatrick   10/3/2011 10:00:20 AM
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I can see a lot of advantages in multicore processors like these.  I wonder though about the fault tolerance for a device that uses two cores and compares the results?  I would think 3 cores and voting the odd one out might be slightly more expensive but better.  Along those same lines the fault tolerance and ability to function in a degraded state might be really useful as well.  Sensor failure or errors related to the sensors need to be accommodated as well in a fault tolerant manner.

I am a bit leary of simply adding in more redundancy.  That can also lead to more failures.  Correct me if I am wrong but 2 controllers with 99% reliability each when coupled are they not then 98% reliable?

In general I learned it was better to design systems with greater reliability, test it and prove it historically in production.  Then only add additional redundancy if it was really required.  Some systems required redundancy as a matter of course in terms of availability for maintenance and mission critical applications.  Perhaps others can weigh in on this and explain this subject a little better.  

I suppose part of this is the diffference between redundant and backup components?  When I served on US Navy ships we had three steam driven turbogenerators for redundancy and a diesel generator for backup.  But we had only one main engine.  I know the costs figure into this as well as they always do.



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