[Pool] Virtualization

lst_hoe02 at 79365-rhs.de lst_hoe02 at 79365-rhs.de
Mon Jul 20 07:29:22 UTC 2015

Zitat von Florian Weimer <fw at deneb.enyo.de>:

> The support.ntp.org site says this about virtualization:
> “NTP server was not designed to run inside of a virtual machine. It
> requires a high resolution system clock, with response times to clock
> interrupts that are serviced with a high level of accuracy.”
> <http://support.ntp.org/bin/view/Support/KnownOsIssues#Section_9.2.2.>
> However, following discussions on this list, there appear to be
> pool.ntp.org instances on Amazon EC2.
> Do the restrictions on virtualization still apply?  I'm pretty sure a
> properly configured KVM host and guest (for example) today has a much
> better hardware clock than most things that were available in the 90s,
> and people were running time servers even back then (even on PCs).

The problem with virtualization is not that it doesn't work at all,  
but you can never be sure. If you have dedicated hardware you are able  
to monopolize CPU to do very accurate counting/timing operations, if  
you are virtualized you are dependant on what you get by the  
Hypervisor. If the Hypervisor is under load it might steel your VM CPU  
cycles without any notice. This is no problem as long as the hardware  
is oversized/not fully loaded, but it might hit you any time. But for  
machines in the pool it should be ok, because the needed precision is  
not that high and the monitor will find machines with repeated  
problems to throw out of the pool.



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