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On 04/25/2013 10:46 AM, Tanstaafl wrote: |
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> On 2013-04-25 10:40 AM, Michael Mol <mikemol@×××××.com> wrote: |
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>> For contrast, having all nodes sync to pool.ntp.org results in time |
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>> variance of up to 2-3 minutes across a dozen or so machines. |
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> |
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> That makes no sense... |
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> |
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> Not calling you a liar or anything, but it just doesn't make sense. |
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> |
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> I can see that it might take each system different times to get fully |
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> sync'd, but for them to consistently vary by this amount? No, something |
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> else is wrong. |
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> |
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> Are these virtualized servers? |
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Some are virtualized, some are hosts, some are standalone. |
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When all machines were configured to speak to pool.ntp.org, the variance |
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was high. Obviously more so any time a guest was using its host's clock, |
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and both guest and host were trying to adjust. |
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There was still significant difference even between standalone systems. |
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pool.ntp.org pulls from a huge pool of timeservers, and there is visible |
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variance between more than a few of them. It's a volunteer effort. |
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*shrug* Unfortunately, I don't have the exact variances in my notes. |
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When I used a single standalone to connect to pool.ntp.org, and had all |
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other systems (standalone, virtualized and guest) connect to that |
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standalone system, virtually all variance went away. The stability of |
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having a single local time source for all but one local machine to sync |
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against overcame the instability caused by having host and guest ntp |
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clients stacked. |
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Of course, ideally, you want VM guests to rely on the VM host for their |
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clock, and have the VM host configured with a good time source. And you |
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would want all bare iron configured to talk to a small pool of tightly |
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synchronized time servers. And if you can trust your layer 2 (or secure |
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your layer 3 with, e.g. ipsec), you may further benefit from setting up |
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a multicast time source. |
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Further, ideally, you want a stratum 1 time server locally. |