[ntp:questions] ARRGH!!! I woke up to a 50 SECOND clock error.
Ron Frazier (NTP)
timekeepingntplist at c3energy.com
Wed Mar 14 15:41:00 UTC 2012
On 3/14/2012 10:41 AM, David J Taylor wrote:
>> Hi David,
>> OK. You asked for it. 8-)
> Well, I actually suggested /all/ the Internet servers being enabled,
> allowing NTP to make its best choice.
>> When I'm through testing, I'll open up the other internet servers as
>> a backup in case the GPS fails. For now, I'm just running with one
>> clock source at a time. Still trying to document and chase down this
>> wandering effect.
>> I ran with NY NIST as the only selectable clock source and monitoring
>> the GPS for comparison all night. The results were horrible. My
>> offsets from NIST time were in the + 65 ms / - 75 ms range. I had
>> the polling interval set to start at 1 minute and go up to 4
>> minutes. There is way too much clock wander to even think about
>> testing the accuracy of the GPS. I've gone back to polling the GPS
>> every 8 seconds as the sole selectable clock source and monitoring
>> the internet servers for comparison. Over the short term, minutes to
>> hours, my GPS, even with NMEA only, is by far the most accurate time
>> source I have. Even if the NMEA signal wanders 70 ms either way over
>> the course of a few days, it won't get any further off than I did
>> using the internet server, and the clock will be much more consistent
>> over shorter time frames.
>> Here are the graphs.
> I'm not surprised that using a single Internet server is worse than
> the GPS/USB, but that's not how NTP is designed to work. With two or
> more Internet servers active, your GPS 50-second glitch would not have
> affected your PC's timekeeping anything like as severely, when you
> have the GPS/USB included to help improve the offset and more like the
> narrow band (about 15 milliseconds wide) shown in:
OK. Here are the loopstats from another computer for 7 days (in the
chart). I don't have any peerstats for it. It has the same server
list. One is preferred. All servers are active. Performance is no better.
(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
such. I don't always see new messages very quickly. If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)
timekeepingdude AT c3energy.com
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