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

  • To: Marco Strullato <marco.strullato@xxxxxxxxx>
  • From: Nico Kadel-Garcia <nkadel@xxxxxxxxx>
  • Date: Tue, 06 Nov 2007 12:43:20 +0000
  • Cc: xen-users <xen-users@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 06 Nov 2007 04:42:37 -0800
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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....


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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