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Re: [Xen-users] dom0 and domU differs after ntpdate

  • To: "Nico Kadel-Garcia" <nkadel@xxxxxxxxx>
  • From: "Marco Strullato" <marco.strullato@xxxxxxxxx>
  • Date: Tue, 6 Nov 2007 13:51:01 +0100
  • Cc: xen-users <xen-users@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 06 Nov 2007 04:51:48 -0800
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After echo 1 > /proc/sys/xen/independent_wallclock
and an ntpdate on each server the time is right.



2007/11/6, Nico Kadel-Garcia < nkadel@xxxxxxxxx>:
Marco Strullato wrote:
> I'm sorry, I think I don't well understand what you wrote. could you
> be more clear?
> why you suggest me not to run ntp on domUs? Maybe I don't know how xen
> works with ntp....
> Thanks
> Marco
All NTP daemons work by manipulating a time offset, an offset between
the clock time reported by the hardware clock and the actual time as
deduced from NTP servers. And they also have a second offset, one that
allows them to retain a record over some period of the amount of drift
that consistently happens and adjust for it. It's described here:


OK? Now imagine that you're a surveyor doing careful work, and you put
some markers down in a convenient place, and you measure how long things
are, and where they are, and you make a nice map, and you record where
your markers very carefully so you can rely on them.

Now imagine some other surveyor starts taking and using your marker, and
*keeps moving it* when you're not looking. You can never hope to get all
your maps done accurately while this is going on.

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