On Wed, May 1, 2019 at 9:56 PM William Herrin <b...@herrin.us> wrote:
> On Wed, May 1, 2019 at 5:48 PM Keith Medcalf <kmedc...@dessus.com> wrote: > >> If you have one such installation, then you really do not care about the >> "accuracy" of the time. However if you have multiple such installations >> then you want them all to have the same time (if you will be comparing logs >> between them, for example). At some point it becomes "cheaper" to spend >> thousands of dollars per site to have a single Stratum 0 timesource (for >> example, the GPS system) at each site (and thus comparable time stamps) >> than it is to pay someone to go though the rigamarole of computing offsets >> and slew rates between sites to be able to do accurate comparison. And if >> you communicate any of that info to outsiders then being able to say "my >> log timestamps are accurate to +/- 10 nanoseconds so it must be you who is >> farked up" (and be able to prove it) has immense value. >> > > If your network is air gapped from the Internet then sure. If it's not, > you can run NTP against a reasonably reliable set of time sources (not > random picks from Pool) and be able to say, "my log timestamps are accurate > to +/- 10 milliseconds so it must be you who is farked up." While my > milliseconds loses the pecking order contest, it's just as good for > practical purposes and a whole lot less expensive. > > And while time source stability is a good criteria, the most important NTP criteria is path latency symmetry between directions. It's better to have a path that is 100 ms of 1-way latency both ways than a path that is 1 ms one way, 100 ms the other way. Rubens
