Tim Shoppa wrote on 14-9-2007 15:00: > The pool system, while not identical to say how ntpd scores and picks its > server > when multiple servers are available, is doing a similar job: attempting to > pick > a server based on its past apparent performance behind the network link. > > We aren't trying to judge accuracy. We're judging sanity and reachability, > and similar to ntpd's internal scoring and selection, round trip time comes > into > play and lowers the score. > > The scoring is not identical to ntpd's, but the end result is the same: High > latency > hurts the score a little bit. > > I know that my two stratum-1 servers are within microseconds of actual time > all > the time, but I do not expect the pool to be the measure of that! > > The pool monitoring tools are very useful for watching latency issues before > they become serious. I really, really appreciate that instead of plotting the > absolute value of the apparent offset, it now plots it as plus or minus. The > sign of > the offset is, I'm told, irrelevant to the score, but it is HUGELY VALUABLE as > a way of making sense of assymetric latencies. > > And an overall point: aren't the graph date/times in terms of UTC? If so, > the asymmetric latency pattern looks EXACTLY like business hours (even > excluding > lunch hour) somewhere in the US (probably closer to the west coast than the > east > coast.)
Thanks for your clear explanation. As I read it you're confirming our earlier conclusion that server admins cannot take much action based on the results of the monitoring system. (That's probably the misconception that triggered this thread) Still I wonder what the value is of a measurement through a single intercontinental link, except for pool users that use that very link. For judging a server for country and continental zones (except the zone the monitoring system is in) this seems even more questionable. Of course things are different as soon as offset > rtt. But since the penalties are small compared to the headroom between the maximum score and the "kick-off threshold", I suppose the issue is academical. As I wrote before, I know ntp, but I'm new to the pool, just trying to understand how it works. It's interesting. Jan _______________________________________________ timekeepers mailing list [email protected] https://fortytwo.ch/mailman/cgi-bin/listinfo/timekeepers
