On 8/12/2010 5:07 AM, Jason Pyeron wrote:
>
> [root@devserver21 ~]# cat /etc/ntp.conf | grep -v ^# | grep -v ^$
> restrict default nomodify notrap noquery
> restrict 127.0.0.1
> server 192.168.1.67
> server 192.168.1.66
> server 192.168.1.65
Some HOWTOs tell you that more time servers is better, on a standard
knee-jerk redundancy theory, but they're ignoring two things.
First, you already have a fallback: the system's built-in clock. It's
perfectly fine to run on that while you ride out your time server's
downtime.
Second, ntpd, internally, is built on a phase-locked loop, which is
supposed to stabilize its time corrections in the face of jitter and
other bad things out in the real world. Like anything based on a
negative feedback loop, however, it can be destablized with certain
inputs. Giving ntpd two or more servers is a pretty good way to
destabilize its PLL in the real, non-ideal world we find on the modern
Internet.
To anyone considering flaming me, please read this first:
http://queue.acm.org/detail.cfm?id=1773943
At minimum, read the section "One server is enough". The bit on PLLs
about halfway down is also directly relevant.
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