[ntp:questions] NTP seems unsuitable for this application... what do you think?

Paul Croome Paul.Croome at softwareag.com
Thu Dec 2 08:46:32 UTC 2004


>If you really care what time it is, leave one of the GPS systems powered 
>up to act as a server.  When synched to GPS it should know to within a 
>few hundred microseconds what time it is and will share its knowledge 
>with anyone who boots up and asks.  If you give an NTP client a stable 
>and accurate source of time, it will synch up and stay synchronized as 
>long as it's powered on, IFF you give it enough time to do so.  It can 
>take twelve to twentyfour hours to achieve tight synchronization from a 
>cold start!  By "tight synchronization" I mean within five milliseconds 
>or less; I've seen Solaris/SPARC systems synchronize with offsets in the 
>low microsecond range.

IIRC, Dave Mills has remarked that the kernel PLL/FLL code in some versions
of Solaris is broken, so that it does not converge optimally during startup
(it's OK under steady-state conditions, though). My observations confirm that.
The bottom line: Don't expect good NTP performance during the first few hours
after coldstart. And BTW, thermal drift as the computers and their crystals
warm up is another factor that means that initial performance will be so-so.


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