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
boxes don't have a direct access to the Internet, so they can't use
public NTP servers to synchronize themselves from. Thus, what I want to
do is to elect a strate 1 server among them and synchronize it using a
hardware clock (GPS or whatever). Then the remaining servers would be
considered as NTP clients and get their time from the strate 1 server.
I believe this configuration is quite acceptable and I make the
assumption that it's going to work well (I can't test because I don't
own any reference clock yet).
Now, for HA purposes, I'd like to see, say, 3 strate 1 servers, working
as peers. The remaining boxes would be configured to use them as
servers (3 "server" entries in ntp.conf for each client).
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.
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.
2/ can you advise me some middle-range clocks (several hundred euros
max.) working on Linux, as well as pros and cons regarding the
technology (GPS, radio...) ?
The Garmin GPS18LVC is inexpensive ~$85 US and is reported to work well.
I use a Motorola Oncore M12+T (no longer made by Motorola but still
available from another manufacturer) ~$200 US (with "evaluation circuit
board" that works very well for me.
The receiver you choose should be designed for timing, not navigation.
It should have a Pulse Per Second (PPS) output.
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