[ntp:questions] NTP in a Linux cluster

Terje Mathisen Terje.Mathisen at tmsw.no
Tue Sep 8 07:34:37 UTC 2009

Lorcan wrote:
> Folks,
> Could any NTP experts suggest how I should best configure NTP in
> a loosely-coupled Linux cluster, where intra-cluster synchronization
> is the top priority?

In this case, the only real answer is to route a GPS+PPS signal to every 
box in the cluster, this will give you ~1-2 us precision for all nodes 
nearly all the time.

If you setup 3-4 independent GPS receivers, and distribute them across 
the servers in the cluster, and let each machine sync to its local 
GPS+PPS signal as well as 4+ machines from the other GPS domains, then 
you would get as a good a sync situation as you can get without going to 
really esoteric solutions (i.e. replacing motherboard crystals with 
TCXOs or Rb standards).

You could setup this with the same configuration file on every machine, 
as long as you include an extra machine from each doamin, so as to 
compensate for those machines already in the list (they ignore 
themselves as source!).

Total cost can be _very_ low if you are willing to do a little work, 
i.e. less than $100 each for 4 Garmin GPS18, plus some cabling and RS232 
signal repeaters/distributors.

The main limitation might well be in the need for a serial port on every 
machine! Many cluster nodes don't have that, in which case you would 
have to fall back on a number of dedicated standalone stratum 1 boxes. :-(


- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

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