[ntp:questions] Re: Reference clocks questions

George N. White III aa056 at chebucto.ns.ca
Fri Jun 23 21:02:04 UTC 2006


On Fri, 23 Jun 2006, Richard B. Gilbert wrote:

> Julien wrote:
>> Hello,
>> 
>> I'm requesting some advice here. I have a bunch of Linux servers
>> (around 20) to synchronize, and I'm planning to use NTP for it. Theses
>> [...]
>> Questions :
>> 
>> 1/ do I need 3 reference clocks (GPS receivers...) for my 3 strate 1
>> servers ?
>
> No.  You can connect the signals from one refclock to three or more servers. 
> Connect the transmit data line from only one of the servers.
> You may need to do some signal buffering since the typical RS232 output is 
> not designed to drive three inputs.

The reason for having multiple servers is that servers are somewhat 
fragile.  You might want to arrange to keep the servers physically far 
apart (e.g., different buildings), in which case cheap GPS units will 
probably cost less than the wiring to connect one server to multiple
servers.

> Having only one refclock makes it a single point of failure.  If it dies you 
> have nothing.  Unless you cannot tolerate a failure, having three refclocks 
> and three servers seems to me to be overdoing it a little. Since you have 
> nothing now, it seems likely to me that you could survive a failure until you 
> could repair or replace the failing component.

The old Trimble at work sometimes stops providing time for a while -- 
could be a software bug. I'd worry that 3 identical GPS's could glitch at 
the same time, so it makes sense to get a couple of the cheapest units and 
one of the next cheapest.  Maybe new units don't have glitches, but since 
they are new nobody has tested them for 10+years.

-- 
George N. White III  <aa056 at chebucto.ns.ca>




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