Re: [gentoo-user] Server system date synchronizaion

[Michael Mol <mikemol@gmail.com>]

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On 04/25/2013 10:46 AM, Tanstaafl wrote:
> On 2013-04-25 10:40 AM, Michael Mol <mikemol@gmail.com> wrote:
>> For contrast, having all nodes sync to pool.ntp.org results in time
>> variance of up to 2-3 minutes across a dozen or so machines.
> 
> That makes no sense...
> 
> Not calling you a liar or anything, but it just doesn't make sense.
> 
> I can see that it might take each system different times to get fully
> sync'd, but for them to consistently vary by this amount? No, something
> else is wrong.
> 
> Are these virtualized servers?

Some are virtualized, some are hosts, some are standalone.

When all machines were configured to speak to pool.ntp.org, the variance
was high. Obviously more so any time a guest was using its host's clock,
and both guest and host were trying to adjust.

There was still significant difference even between standalone systems.
pool.ntp.org pulls from a huge pool of timeservers, and there is visible
variance between more than a few of them. It's a volunteer effort.
*shrug* Unfortunately, I don't have the exact variances in my notes.

When I used a single standalone to connect to pool.ntp.org, and had all
other systems (standalone, virtualized and guest) connect to that
standalone system, virtually all variance went away. The stability of
having a single local time source for all but one local machine to sync
against overcame the instability caused by having host and guest ntp
clients stacked.


Of course, ideally, you want VM guests to rely on the VM host for their
clock, and have the VM host configured with a good time source. And you
would want all bare iron configured to talk to a small pool of tightly
synchronized time servers. And if you can trust your layer 2 (or secure
your layer 3 with, e.g. ipsec), you may further benefit from setting up
a multicast time source.

Further, ideally, you want a stratum 1 time server locally.


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