State of the microserver HOWTO
Gary E. Miller
gem at rellim.com
Tue Jun 7 19:54:18 UTC 2016
On Tue, 07 Jun 2016 21:13:56 +0200
Achim Gratz <Stromeko at nexgo.de> wrote:
> Gary E. Miller writes:
> > "On startup ntpd will take the first time it gets to set the system
> > clock. If this first time is an imprecise clock, say derived from
> > NMEA, then ntpd may takes days to restabilize.
> > The first time ntpd acquires will tend to be the ones higher up in
> > the file with the lowest maxpoll.
> > So to work around this ntpd glitch put your best time sources high
> > in the ntp.conf file, with your shortest maxpoll and your worst one
> > at the bottom with higher maxpolls."
> This is quite likely wishful thinking.
Nope, and I'ver got the data to prove it.
> Provided that DNS is working
> as it should,
I never use DNS in my ntp.conf files. Too many problems.
> all servers get mobilized essentially at the same time
> (you can check the logs in which order they get contacted)
Yup, done that. The ones higher in the ntp.conf file, and the ones
with the smaller maxpoll tend to get called sooner than the rest.
Not always, but usually.
> and the
> first one to actually pass the quality filters is the one that sets
> the time.
Or rather, some small subset of the quality filters. It does not
appear the full clustering/grouping thing is done before selecting
the one winner.
> I don't know about GPS, but with DCF77 all network clocks
> have stabilized before I get the first reading from the stratum 0
> clock no matter where I put these entries in the config file.
With my PPS at the top of the file and minpoll 4 the PPS almost always
wins the race. This with gps already running and stable.
> Maxpoll settings don't kick in until much later.
I see it as soon as I start ntpd.
> The quality filters
> do prefer local peers over remote ones,
Not that I can see. Only if they have lower jitter. So the PPS
usually gets used, but not the NMEA. If I'm not careful the PPS
can get outvoted my local network chimers.
> it'll usually lock to my
> router first before the stratum 1 servers from the PTB kick in a few
> seconds later (I've hard-configured these since they are the ones
> providing the time for DCF77).
Sounds like you are not using the mode 28 refclock. I find it perfoms
better than the other refclocks with PPS. It certainly does not have the
startup issue you mention.
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem at rellim.com Tel:+1 541 382 8588
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