[time-nuts] Recommendations for NTP server
jpp at cloudview.com
Sun Apr 23 18:09:33 EDT 2006
Geoff Powell wrote:
> In article <444BF2D0.40603 at cloudview.com>, John Pettitt
> <jpp at cloudview.com> writes
>> I'll second the soekris box - my box time.no-such-agency.net is a 4801
>> running FreeBSD with a GPS18LVC. You can expect offsets in the +/-
>> 5us range except when the box is stressed - the standard xtal in the box
>> is not temperature compensated so offsets will spike to as much as 250us
>> when the system does something compute intensive. If you don't need the
>> HD consider the 4501 as it has the ability to timestamp a PPS using
>> internal counters rather than the DCD kludge. - Again see phk's
>> excellent work on the subject including the code in FreeBSD to support
>> PPS on a 4501.
> So you'd recommend a 4501, with FreeBSD in Compact Flash? I wanted to
> use CF anyway, since a box running 24/7 is not the best environment in
> which to have moving parts. The box will have no more that NTP and MRTG
> on it.
> Thanks for the accuracy estimate.
Yes it the 4501 is really good for this (it's also less expensive) - see
http://phk.freebsd.dk/soekris-pps/ and this
http://phk.freebsd.dk/soekris/kern45xx.html for info on the subject.
The real win with the 4501 is using the built in counters in the Elan
CPU to latch the PPS signal - this takes all the interrupt latency stuff
out of the mix and improves the accuracy considerably - the stability of
the oscillator will be your biggest source of errors. If you run
nanobsd (basically a cut down FreeBSD) with no jobs other than NTP on
the box you should get a really nice server for under $300 including the
GPS. You might want to think about running mrtg on another box (unless
you are willing to put the data on ram disk and lose it on power cycle)
as the CF card won't like being written repeatedly for log and graph
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