Date: Mon, 7 May 2007 15:15:59 -0500 From: "illoai@gmail.com" <illoai@gmail.com> To: "Chuck Swiger" <cswiger@mac.com> Cc: RW <fbsd06@mlists.homeunix.com>, freebsd-questions@freebsd.org Subject: Re: Time Synchronizing Between Two Servers Message-ID: <d7195cff0705071315x54a2173ch1f487f60f24a4015@mail.gmail.com> In-Reply-To: <7967B2A8-3FF5-46AD-AFEA-9EE5C680A414@mac.com> References: <20070503014137.I3544@duane.dbq.yournetplus.com> <a969fbd10705021849g64f4752fobd5b6a817254ba28@mail.gmail.com> <20070503015723.S3544@duane.dbq.yournetplus.com> <d7195cff0705022217k4f0aaf2fibd2bfeb97b6498c8@mail.gmail.com> <4639FAB6.9050701@mac.com> <20070504171053.41eddb6a@gumby.homeunix.com> <7967B2A8-3FF5-46AD-AFEA-9EE5C680A414@mac.com>
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On 07/05/07, Chuck Swiger <cswiger@mac.com> wrote: > On May 4, 2007, at 9:10 AM, RW wrote: > > On Thu, 03 May 2007 11:07:34 -0400 > > Chuck Swiger <cswiger@mac.com> wrote: > >> Sun SPARC machines have good HW clocks, and also some of the newer > >> Macs also seem to have consistently low values in ntp.drift and > >> handle timekeeping well. > > > > Does that matter? > > A good question-- the answer seems to be that it depends. A low value in ntp.drift is inconsequential compared to a constant or near constant value, which many motherboards do not "support". > > > The RTC time is almost immediately overridden by ntpdate. The > > drift is a systematic error that ntpd allows for. I would > > have thought that the only significant issue, is whether the system > > loses timer interrupts under load. > > There are limits to how rapidly ntpd will slew the clock via adjtime > (); the smaller the intrinsic drift of the HW clock, the sooner any > adjustment (beyond the initial stepping at system boot via ntpdate) > will complete. This only matters to stratum-2 and higher systems-- > anything with a primary reference clock (GPS/WWV/ACTS/etc) is going > to sync to that and ignore the local HW clock entirely. If you really need that ultimate precision, by all means ntpd -> ntpd on the LAN is probably the Right Thing, in conjunction with close temperature control. For most uses (keeping two or more given machines within 10ms or so on the same LAN) timed with one machine synced to the outside world via ntpd is simpler at the very least. -- --
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