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From André Warnier ...@ice-sa.com>
Subject [OT?] Re: Multiple data centers and redundency?
Date Wed, 26 Aug 2009 22:43:55 GMT
Jeffrey Janner wrote:
> George -
> This is why I hate statistics.  You can make them say anything.

I was thinking the same thing, remembering the recent financial troubles.

1/( (2 hours)/24(Hours day) * 1/(3*365))/2 (Data centers)

- customers don't work 24 hours a day, they usually work 8 hours a day
- they also don't work 365 days/year, more usually like 200
- data center failures are not necessarily uncorrelated with eachother 
nor with the above (no more than one bank failing is uncorrelated to 
another one failing)

On the other hand, maybe the application is such that one customer 
losing his session could precipitate another global financial meltdown...
;-)

I would add that, no matter what the OS DNS resolver does with 
time-to-live for an address translation, another factor to consider is 
that a lot of software asks the DNS resolver for an address once, then 
stores it internally forever and never asks again.
I am just mentioning that in view of the likely expense to set up this 
whole thing, and then relying on a "DNS load balancer" (?) to switch 
from one to the other center ?


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