Date: Mon, 7 May 2007 23:02:46 +0100 From: RW <fbsd06@mlists.homeunix.com> To: freebsd-questions@freebsd.org Subject: Re: Time Synchronizing Between Two Servers Message-ID: <20070507230246.198b6608@gumby.homeunix.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 Mon, 7 May 2007 12:30:29 -0700 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. > > > 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. As I understand it, ntpd uses it's own kernel interface, ntp_adjtime(), which lets it share some of its internal state with the kernel. The kernel knows about the time and frequency errors, and makes the corrections itself every second. If the time error is zeroed by ntpdate, and there's a drift-file, I don't see that the actual drift value makes much difference. I suspect that any quartz clock is overkill.
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