[ntp:questions] ntpd wedged again

David J Taylor david-taylor at blueyonder.co.uk.invalid
Wed Feb 15 08:31:53 UTC 2012


> The problem with THREE GPS receivers, or just about any other clock, is 
> that it it can too easily degenerate to the two server case.  It is well 
> known that "a man with two clocks can never be certain what time it is."
>
> Four, five, and seven are the magic numbers for a robust configuration.
> Most sites will settle for four.  The very paranoid or the very rich 
> might go for seven.

I'm not rich, so I'm using Garmin GPS 18 and Sure Electronics receivers. 
Each stratum-1 server has one GPS receiver, plus a number of other servers 
including at least three Internet servers, and two local PC servers, 
making a reasonably robust configuration.

In the event that I lost both the Internet connection and one GPS 
receiver, then I am still confident that the two remaining GPS receivers 
will be near enough that a client PC selecting one or the other server to 
sync to will still be well enough within time for my purposes.  In the 
event of GPS going down altogether, we'll have more problems to deal with!

David 



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