Hi Tobias, sorry for the late reply. Your email via the mailing list just arrived in my mailbox.
Tobias Gierke wrote: > Hi everyone, > > I'm facing a NTP-relateded challenge at work and hope that somebody on > this list has maybe solved a similar problem already: > > - Our product is a system consisting of multiple components that may or > may not run on the same host and all parts require time synchronization > at all times because we're processing timestamped measurement data A basic question is: Which accuracy is required for your application? > - Our application does a lot of heavy computation triggered at the start > of every minute (by crond) > - Since a lot of different application versions are deployed in the > field and customers are slow to upgrade, we need to test many different > versions of our application in our lab > - To ease hardware requirements for testing we run all those different > versions of our application inside virtual machines, currently all > synced to the same NTP server The next question is: Which virtualization software do you use? How accurately the system time can be synchronized depends strongly on the type and version of the virtualization software. > - Since all those VMs are synchronized to the same server, all cron jobs > on those VMs kick in at the same time, overloading the VM host periodically Yes, and the the VMs can easily loose time. > I already looked into a simple solution (like being able to pass some > magic "--offset XX seconds" option to ntpd) but it seems there is no > such thing. There is no such thing when you specify remote NTP servers. It is possible, however, to specify a time offset for hardware reference clocks (i.e. server 127.127.x.y). > > So my current idea is to > > 1.) have 4 different time servers that each are offset from all the > others by 15 seconds (so server #1 would have offset 00 seconds, server > #2 would have offset 15 seconds, etc.) > 2.) configure those servers with ULC w/ PPS and hook-up the same PPS to > all 4 servers OR have one PPS source for each server and have all of > them sync to a common source (like a DCF77 time signal) > > My problems are with the second step: I don't have a PPS source, I only > have a Meinberg DCF600 USB > (https://www.meinbergglobal.com/english/products/usb-dcf77-clock.htm), > but I couldn't find any documentation on how to use it as a PPS source > only (and ignore the actual "time" part of the synchronization). Actually, the DCF600USB doesn't provide a 1 PPS output by default because the accuracy derived from the standard DCF77 AM signal is anyway about a few milliseconds only. You get this level of accuracy also via the driver software, and unlike with GPS receivers an additional 1 PPS signal doesn't significantly improve the accuracy in this case. > Furthermore I don't really want to buy 3 more of those clocks if I can > help it (especially considering the fact that we might need even more > different "time domains" as the number of VMs increases). The DCF600USB provides a 1 PPS signal internally, which can be easily made available to the outside world. If you want you can give me a phone call so we can discuss how you could do this. Please find my phone number below. Regards, Martin -- Martin Burnicki Senior Software Engineer MEINBERG Funkuhren GmbH & Co. KG Email: martin.burni...@meinberg.de Phone: +49 5281 9309-414 Linkedin: https://www.linkedin.com/in/martinburnicki/ Lange Wand 9, 31812 Bad Pyrmont, Germany Amtsgericht Hannover 17HRA 100322 Geschäftsführer/Managing Directors: Günter Meinberg, Werner Meinberg, Andre Hartmann, Heiko Gerstung Websites: https://www.meinberg.de https://www.meinbergglobal.com Training: https://www.meinberg.academy _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
