Mike K Smith wrote: > On 12 May, 15:16, "Richard B. Gilbert" <[EMAIL PROTECTED]> wrote: >> Mike K Smith wrote: > >>> Looks like I should be reducing maxpoll. I guess the design of NTP is >>> optimised for clocks with predictable drift rates, and a sudden >>> variation in drift rate takes longer to correct. >> You DO know that NTPD adjusts the poll interval to fit the current >> conditions??? It will increase the poll interval to MAXPOLL only when >> the clock is stable and very close to being correct. The default values >> of MINPOLL and MAXPOLL are correct for all but the weirdest cases. > > I know that ntpd adjusts the poll interval to fit the current > conditions, but I am describing a case where the current conditions > changed. The clock had been stable for around a week, and the polling > interval had increased to 1024 seconds, then something changed. It > looks like the clock started drifting by about 2ppm, the poll interval > didn't change for three hours causing a 15ms offset before beginning > to correct the drift. > I initiated this thread to help me understand why ntpd took so long to > respond. I had expected to see the poll interval decrease and the > offset swing back towards zero after the first couple of polls showed > the increased offset. > >> Are you operating your machines in a controlled (temperature) >> environment? If the temperature bounces around, so will your clock. >> NTPD will correct it but if the temperature drops five degrees in five >> minutes when the air conditioning kicks in, NTPD may have a little >> difficulty keeping up. > > The systems are in air-conditioned equipment rooms, I wasn't expecting > to frequency changes due to temperature.
Do you monitor the temperature? Many data centers have a clock driven chart recorder that records the temperature and humidity. If the temperature changes the clock WILL be affected I can't tell you why NPTD took "so long" to jump on a 15 millisecond error, that's a problem for the mathematicians/control systems theory guys. If you need synchronization and/or accuracy closer than that, you may need: a. Better environmental control/monitoring, or b. A better clock (OCXO, TCXO). This could get expensive; computer clocks use basically the same mechanism as a cheap "quartz" wristwatch but lack the temperature control that usually keeps the wristwatch somewhere near 98.6 degrees Fahrenheit. Would you be upset if your wristwatch gained or lost thirty seconds per month? c. A different tool than NTPD for the job. Some people advocate a tool called "chrony", something with which I have no experience! _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
