[ntp:questions] Meinberg NTP monitor, silly question
Richard B. Gilbert
rgilbert88 at comcast.net
Tue Dec 22 21:00:36 UTC 2009
> On 2009-12-22, Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
>> unruh wrote:
>>> On 2009-12-22, Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
>>>> David J Taylor wrote:
>>>>> "G8KBV" <g8kbv at nospam-uko2.co.uk> wrote in message
>>>>> news:MPG.2599f4f8b90958d1989692 at news.demon.co.uk...
>>>>> You will find that for the best performance, the NTP PC needs to be left
>>>>> running, as initial settling is not quick.
>>>> "Not quick" is an extreme understatement! It takes about 30 minutes to
>>>> get a "reasonable approximation". It can take ten to twelve hours to
>>>> stabilize with the best possible approximation of the time. Once there
>>>> it's good for as long as you can keep the power on and the temperature
>>>> reasonably stable.
>>> Yes, the time scale is about 1 hour half life (it takes about 1 hour to
>>> halve the error). David Mills gets really
>>> annoyed if someone points out how slow ntp is at converging. It is
>>> definitely a feature, not a bug. That you or I could, with the first
>>> three offset measurements, make a far better approximation to the true
>>> time and rate than ntp does, is irrelevant.
>> Well, you could always try to create an NTPD that would converge more
>> quickly without introducing some other nastiness. Somehow I think this
>> would be a massive project and is quite likely impossible. If Dave
>> Mills thinks it won't work he's probably right.
> As I said, it has already been done. It is called chrony. And it works--
> about three times better accuracy than ntpd in the tests I ran, and far
> far faster convergence. It impliments an almost complete ntpd 3.0
> standard,(without broadcast option, but as of 1.24-pre1 with refclock
> support). It does not work on Windows machines.
> David decided on a simply Markovian feedback loop with one single
> "memory"-- the current rate. It is simple, easy to analyse ( although
> with the additional bells and whistles like the clock filter, the huff
> and puff filter, stepping, etc, it is far more difficult to analyse),
> and has been tested extensively. That does not mean it is the best
> way of using the data, and certainly as far as rate of convergence
> is concerned it is far from the best.
>> Keeping an NTPD server up and synched is not all that difficult. A UPS
>> will keep you alive for three to fifteen minutes if power fails. The
>> longer the UPS run time, the more it costs. Any longer than fifteen
>> minutes and you will need a generator fueled by either gasoline or
>> natural gas. You will either need a human being to start it and set it
>> for the right speed or a device that will do this automagically.
> Lets see, Pay a few $100 for a UPS (and many more for a generator) ,
> run the machine 24/7 with the associated energy costs, or load a free
> program. Hmm.
Most computers that need accurate time live in a data center somewhere
and shut down maybe as often as once every six months! I've had a few
machines that ran continuously for a year or more! It's not impossible;
it just requires a lot of luck OR heavy expenditures for a UPS, a backup
generator, N+1 redundant air conditioners, etc, etc. Some enterprises
require this sort of uptime and are prepared to pay the bills.
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