[ntp:questions] NTP servers redundancy

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Tue Jan 19 12:41:06 UTC 2010

In article <1245298544.863191263816061789.JavaMail.root at spooler9-g27.priv.proxad.net>,
 jthu at free.fr writes:
>Hello everybody,
>for a ship project, we've got a LAN with two NTP servers
 synchronised by a masterclock, itself synchronized by GPS.
>The idea was to have redundancy between the 2 servers, to
 ensure continuous synchronization to the clients in case
 one of the server went down.

What sort of thing is your master clock?  Does it speak NTP?
If not, how does the timing info get from the master to the
NTP servers?

How many systems are going to be using your NTP servers?
What sort of accuracy do you need?  What sort of reliability?

Suppose you only had one server.  How long would it take to
fix it if something went wrong?  How expensive would that be?
(In terms of lost data rather than just the cost of fixing it.)

>I wonder now if the dual NTP source architecture is the good one :

Maybe, but maybe not.

In general, 2 is a nasty number for ntp.  How do you tell which one
is better?

One server is simpler and easier to understand.

>Is the "clock hopping" resulting of this dual architecture a real problem ??

Probably not.  That's the sort of thing you have to try.

You should also try seeing what happens if you only have one server
and it gets unplugged.

In general, if a system has been up for a while (day or two) it
will coast if it can't contact any servers.  That coasting may
be good enough.  It will drift more if the temperature changes.

>Does the NTP algorithm enable that when a server go down
 (or is no more synchronized), its clients switch easily
 to the second one, without any visible synchronization interruption ?? 

>Will it be "transparent" for the clients when the first server will be back ?

If one dies, the clients will switch to the other one.  Maybe they
won't do it as fast as you would like.

There may be hiccups.  It depends on how accurate you need the time
to be.

>How shall be the clients configured for this architecture ??

  server host1
  server host2

>Thanks a lot for your help.

These are my opinions, not necessarily my employer's.  I hate spam.

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