[ntp:questions] iburst

David Woolley david at djwhome.demon.co.uk
Mon Nov 27 07:34:27 UTC 2006


In article <%crah.14971$Uz.9028 at trnddc05>,
terrypearl <fastsnip-bcard at yahoo.com> wrote:

> driftfile: -21.719

> good? bad ? indifferent ?

Without knowing the frequency error of the timing crystal in the PC, it's
impossible to say.

What was meant by the question was:  does the value in your driftfile 
accurately reflect the correction needed to maintain the steady state?

Because you are not keeping the machine up for very long at any one time,
it is possible that the drift value never properly converges, so the
value is not particularly accurate.  If you didn't have a drift file at
all, or if it is unreadable to ntpd, ntpd would have spent about 15
minutes trying to calculate the frequency error, before setting the
time.  However, I'm not really sure how you define "achieve synch".

(Also, as you say you use Linux, Linux shares, with Windows, a tendendency
to lose clock interrrupts, which can severely disrupt the ability to maintain
accurate time.)

Incidentally, although I haven't tried it in anger, I believe that a system
with a good driftfile value will achieve low offsets faster if it is 
started with an offset of more than 128ms.  Below that, gentle corrections
are applied, but, above it, a step correction is applied.

As to leaving the machine on, that is very good advice for precision time
synchronisation protocols, like NTP.  We cannot know when people are
under severe financial constraints if they don't tell us.




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