Re: [ntp:questions] Meinberg NTP Software--Time Accuracy
David J Taylor david-tay...@blueyonder.not-this-part.nor-this.co.uk.invalid writes: Richard B. Gilbert wrote: W. eWatson wrote: [] What sort of accuracy might I expect from my 4 servers, as mentioned above? Are those servers applicable to any site in the USA or Canada? [] Assuming reasonably good servers with low delay, I would expect to get +/- 10 milliseconds or better. The absolute best you will be likely to see occurs between 1AM and 6AM local time; the world (your part of it) is asleep, the net is unbusy. . . . +/- 10 milliseconds using what client OS? I ask as I haven't seen it that good here with Windows (which is what the OP has, I believe). With Linux you should get better than 1ms. With Windows from what I have read 10ms is achievable depending on your network loads, etc. David ___ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
Re: [ntp:questions] Meinberg NTP Software--Time Accuracy
Unruh wrote: [] With Linux you should get better than 1ms. With Windows from what I have read 10ms is achievable depending on your network loads, etc. I would be interested to know what configuration allows Windows to achieve +/- 10ms - it's something I've never seen here on cable modem connected systems, with just Internet sources, using the default polling intervals which allow as long as 1024s between polls. Do you happen to have a reference? On the other hand, using a LAN connection, and a 64s maximum polling interval, I regularly see +/- 1.5ms with Windows 2000, XP, Vista (*) and Windows 7. (*) not when I run a rather ill-behaved hardware and software combination, though. Cheers, David ___ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
Re: [ntp:questions] NTP - best practice if there is a local stratum 2 server
Dave f...@coo.com wrote: I assume, for absolute accuracy (which is not important here, but I'm intersted), this is going to be better than any attempt to set the time from the ntp pool. Is that correct? You never know that. What you get from the pool may be a stratum-1 server locked to GPS time on a fast unloaded connection, or it may be a slow box on a saturated ADSL line and synchronized to time.windows.com. Your local server will be better to depend on. You at least know what you get, and/or you can ask the department it belongs to what quality you can expect. You can never do that with the pool. But setting the time from the local server is also going to be cause a problem if that server fails for some reason. True. Is there any way to make use of a local server if it's working, and then use the pool if its not? Of course. When you configure the local server as a prefer server, it will usually work out that way. To be honest, this is all a bit academic, as there is no real practical need to have an accuracy of better than a minute or two on these machines. In fact, an hour wrong would not make much difference but it might irritate a few people. But it is important the two machine agree with each other, as otherwise files appear to be created in the future by a few ms, which screws up the 'make' program some times. Then you should, as you do, synchronize one to the other or both of them to the same (local) third server. ___ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
Re: [ntp:questions] NTP - best practice if there is a local stratum 2 server
Dave wrote: I'm trying to set up the time on a couple of machines at the University of Washington and have tried two ways: 1) Sync both to the ntp pool - not very successful, as they kept differing by enough to cause 'make' to say files were created in the future by a few ms - no doubt due the NFS exported drives. 2) Set one via ntpd (call is master) from the ntp pool, then the other local machine (slave) read the time from the master. That appears to work quite well. They at least agree on the time pretty closely now. The absolute accuracy might not be as good as possible with a local time server, but for practical purposes it works well. Searching around, I found that the university does in fact have their own strtatum 2 time server - I assume in another department to where the machines I'm using are located. The server is bigben.cac.washington.edu I assume, for absolute accuracy (which is not important here, but I'm intersted), this is going to be better than any attempt to set the time from the ntp pool. Is that correct? Accuracy should be in the very low milliseconds; e.g. plus or minus five milliseconds. You should configure a minimum of four timeservers using systems near you in net space. A system may be physically within a few hundred yards and still be several miles away as far as signal transmission is concerned. But setting the time from the local server is also going to be cause a problem if that server fails for some reason. That's one of the reasons why you are advised to configure four or more servers! Is there any way to make use of a local server if it's working, and then use the pool if its not? Configure four servers and you can survive the loss of one. Configure five and you can survive the failure of two. Configure seven and survive the failure of three. Failure can mean either incorrect time or just not responding to queries. To be honest, this is all a bit academic, as there is no real practical need to have an accuracy of better than a minute or two on these machines. In fact, an hour wrong would not make much difference but it might irritate a few people. But it is important the two machine agree with each other, as otherwise files appear to be created in the future by a few ms, which screws up the 'make' program some times. The machines should agree with each other reasonably well; e.g. within a hundred or two hundred microseconds. You MAY get better than that but remember that keeping time was not, and will not be, very high priority in the design of any computer system. With some you may consider yourself lucky if the date is correct. It's easier to get and keep close synchronization if you have have some sort of a hardware reference clock such as a GPS timing receiver, a WWV receiver, etc. GPS timing receivers are available from $100 US and up. The bottom of the scale is a bare circuit board. Moving upscale you can get PCI cards, stylish tabletop devices, rack-mount equipment, etc. For about $1200 US you can get a clock on a PCI card that will plug into your computer. It will have an oven controlled crystal oscillator and provision for a GPS input. Talk to Symmetricomm and/or Meinberg Funkurhren; both have such hardware available. ___ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
Re: [ntp:questions] NTP - best practice if there is a local stratum 2 server
Dave wrote: But setting the time from the local server is also going to be cause a problem if that server fails for some reason. What I do here (in my home network) is make the NFS server also an NTP server, and make sure that the NFS clients prefer the NFS/NTP server over any others. (In fact: I configure those NFS clients to have only one NTP server, and that's the NFS server). This way, as long as the NFS server is up, chances are that its NTP server will also be up. Cheers, Jan ___ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
Re: [ntp:questions] NTP - best practice if there is a local stratum 2 server
Hi, Dave wrote: I'm trying to set up the time on a couple of machines at the University of Washington and have tried two ways: 1) Sync both to the ntp pool - not very successful, as they kept differing by enough to cause 'make' to say files were created in the future by a few ms - no doubt due the NFS exported drives. 2) Set one via ntpd (call is master) from the ntp pool, then the other local machine (slave) read the time from the master. That appears to work quite well. They at least agree on the time pretty closely now. The absolute accuracy might not be as good as possible with a local time server, but for practical purposes it works well. Searching around, I found that the university does in fact have their own strtatum 2 time server - I assume in another department to where the machines I'm using are located. The server is bigben.cac.washington.edu I assume, for absolute accuracy (which is not important here, but I'm intersted), this is going to be better than any attempt to set the time from the ntp pool. Is that correct? But setting the time from the local server is also going to be cause a problem if that server fails for some reason. Is there any way to make use of a local server if it's working, and then use the pool if its not? To be honest, this is all a bit academic, as there is no real practical need to have an accuracy of better than a minute or two on these machines. In fact, an hour wrong would not make much difference but it might irritate a few people. But it is important the two machine agree with each other, as otherwise files appear to be created in the future by a few ms, which screws up the 'make' program some times. Init file is /etc/inet/ntp.conf Make it easy, sync them all to a ntp server, internal or external should not matter for the simple use you plan for(make) You have time.apple.com for instance and tick tock server tick.usnogps.navy.mil server tock.usnogps.navy.mil and nasa ntp.nasa.gov and many more /michael ___ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
