[154316] in North American Network Operators' Group
Re: [c-nsp] NTP Servers
daemon@ATHENA.MIT.EDU (Jimmy Hess)
Sun Jul 1 22:00:15 2012
In-Reply-To: <CAJAdsDnEovwn9A1sP1T8cd5x1pzrM8khwrVJb7LiwMNP9aOZ9g@mail.gmail.com>
Date: Sun, 1 Jul 2012 20:59:42 -0500
From: Jimmy Hess <mysidia@gmail.com>
To: PC <paul4004@gmail.com>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On 7/1/12, PC <paul4004@gmail.com> wrote:
> If your application requires sub-5 second accuracy, (such as end of a
> banking day), then Windows NTP is unsuitable for the purpose.
Looks like CYA on Microsoft's part.
That i've seen, Windows NTP in physical environments with a hardware
system clock not having issues consistently provides accuracy better
than +/- 0.5 against the time source it's synced with, but in
virtual environments, which have incompatibilities with high
sub-second RTC accuracy in the first place, neither Windows nor Unix
NTP services are able to provide that consistently without much
tinkering.
If it's absolutely critical that you have sub-5 second accuracy,
even Unix NTP is not to be considered good enough, you need highly
accurate hardware time source, something more accurate than the usual
system clock you find in a PC or server. Unix NTP can only do so much
to correct for a broken system clock; although it does do a very
good job disciplining PC real-time clocks that consistently run a bit
too fast or too slow, ultimately the
personal computer clocks can at times be unreliable....
If they were perfect, you wouldn't need time sync in the first place;
just set them once,
and correct the annual 0.01 seconds worth of error once a year....
--
-JH
