Cost-effectivenesss of highly-accurate clocks for NTP

Fri May 13 21:01:21 UTC 2016

Den 13. maj 2016 21.40 skrev "Eric S. Raymond" <esr at thyrsus.com>:

> Traditionally dedicated time-source hardware like rubidium-oscillator
> GPSDOs is sold on accuracy, but for WAN time service their real draw
> is long holdover time with lower frequency drift that you get from the
> cheap, non-temperature-compensated quartz crystals in your PC.
>
> There is room for debate about how much holdover you should pay for,
> but you'll at least be thinking more clearly about the problem if
> you recognize that you *should not* buy expensive hardware for
> accuracy.  For WAN time service, in that price range, you're wither
> buying holdover and knowing you're doing so or wasting your money.

Ok how many hours or days of holdover can you expect from quartz,
temperature compensated quartz or Rubidium? Should we calculate holdover as
time until drift is more than 1 millisecond, 10 ms or more for NTP
applications?

I am thinking that many available datacenter locations will have poor GPS
signal so we can expect signal loss to be common. Some weather patterns
might even cause extended GPS signal loss.

Regards

Baldur