Date: Mon, 7 May 2007 12:30:29 -0700 From: Chuck Swiger <cswiger@mac.com> To: RW <fbsd06@mlists.homeunix.com> Cc: freebsd-questions@freebsd.org Subject: Re: Time Synchronizing Between Two Servers Message-ID: <7967B2A8-3FF5-46AD-AFEA-9EE5C680A414@mac.com> In-Reply-To: <20070504171053.41eddb6a@gumby.homeunix.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>
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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. 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. -- -Chuck
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