Re: [SAGE] number of eggs in a basket

[John Sechrest <sechrest@jas.peak.org>]

Ruth Milner <rmilner@nmt.edu> writes:

 % Any system goes down from time to time, whether planned or not,
 % due to hardware/software/power upgrades/failures/etc. If you
 % distribute 10 services across 10 servers instead of one, it is 10
 % times more likely that some sort of hardware or system software
 % problem will take out a service. The clients will therefore see
 % more outages overall. Of course, with modern computers, that
 % probability for a single system is very small; but it may go
 % from negligible to measurable when multiplied by 10 or more.

 We know from Pattersons work that 90% of outages are a result
 of mis-steps by system administrators. 
 So adding 10 times the hardward does not mean that the 
 number of outages will go up by a factor of 10.

 And if you simplify the configuration issues by eliminating
 interdependencies, then in fact while the hardware oriented
 outages may go up by a factor of 10, the over all outages
 may actually go down. 

 So this is more complex than presented. 



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