[ntp:questions] Magice Server Numbers: 4,5,7,9

Richard B. Gilbert rgilbert88 at comcast.net
Fri Sep 16 03:44:39 UTC 2011


On 9/15/2011 10:34 PM, Doug Calvert wrote:
> Hello,
>   From time to time people mention that the magic number of servers is
> 4,5,7 and nine. However I can not find a reference or explanation for
> the magical properties. Can anyone explain the background/basis in
> general? And specifically how is five or seven preferable to six?

Okay!  It looks as if you read something I posted here.

1.  A man with two clocks can never be certain what time it is!
2.  Three clocks are the minimum necessary to get reasonably good and 
reliable time.
3.  The weakness of three clocks is that the failure of any one clock
     leaves you with case 1.
4.  Four clocks is the minimum robust configuration.
5.  Five clocks allows for two failed clocks.
6.  Seven clocks allow for the failure of three.
Etc, etc. . . .




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