----- Original Message ----- > From: "Michal Skrivanek" <michal.skriva...@redhat.com> > To: "Shahar Havivi" <shah...@redhat.com>, "Alon Bar-Lev" <alo...@redhat.com> > Cc: vdsm-devel@lists.fedorahosted.org > Sent: Monday, April 6, 2015 4:31:44 PM > Subject: Re: [vdsm] vdsm hosts clock sync > > > On 6 Apr 2015, at 14:05, Shahar Havivi wrote: > > > On 06.04.15 08:00, Alon Bar-Lev wrote: > >> > >> > >> ----- Original Message ----- > >>> From: "Shahar Havivi" <shah...@redhat.com> > >>> To: "Alon Bar-Lev" <alo...@redhat.com> > >>> Cc: vdsm-devel@lists.fedorahosted.org > >>> Sent: Monday, April 6, 2015 2:54:07 PM > >>> Subject: Re: [vdsm] vdsm hosts clock sync > >>> > >>> On 06.04.15 07:50, Alon Bar-Lev wrote: > >>>> > >>>> > >>>> ----- Original Message ----- > >>>>> From: "Shahar Havivi" <shah...@redhat.com> > >>>>> To: vdsm-devel@lists.fedorahosted.org > >>>>> Sent: Monday, April 6, 2015 2:44:06 PM > >>>>> Subject: [vdsm] vdsm hosts clock sync > >>>>> > >>>>> Hi, > >>>>> > >>>>> I want to add a new feature that reports migration actual downtime (the > >>>>> time > >>>>> that the VM was inaccessible to the user). > >>>>> > >>>>> Libvirt reports that information but the vdsm hosts need to be in sync > >>>>> by > >>>>> clock > >>>>> time. > >>>>> I can measure the ping for NTP server an report back to the user if the > >>>>> ping > >>>>> is too long (more then ~100ms or so) - a way to do that is via ntpstat > >>>>> shell > >>>>> command. > >>>>> The NTP delay can be report back via vdsStats and can be performed > >>>>> every > >>>>> few hours or so. > >>>>> > >>>>> Anyone knows of a better way that we can sync between hosts? > >>>> > >>>> I am unsure how a ping to clock source is helping, can you please > >>>> explain > >>>> more? > >>> In this case I can only report back to the user that its hosts clock is > >>> delayed and need to be set… > > I had in mind that hosts are synchronized by NTP and we report the difference > between local time and the reference (NTP) time, i.e. what "ntpstat" returns > This way we don't need to ping around or compare directly all the hosts, but > we can rely on the same source and individual hosts's awareness of accuracy > > >>>> > >>>> If you assume clocks are synced why anything more is needed? > >>> Why do I assume that? > > the feature requires those 2 hosts to have same clock, not necessarily the > correct one. But I believe having all hosts sync to the actual time is > beneficial on its own > > >>>> > >>>> Or would you like to have a solution in which you do not require clock > >>>> sync? > >>> > >>> I do need the clock to be in sync - if not libvirts "actual downtime > >>> migration" will be not accurate. > >> > >> you do not need clock to sync, you need to know the delta between hosts. > > the libvirt API uses the delta internally so we can't use only that. Also I > think it is easier to have clock synced by a tool designated for that > > >> > >> but if you assume clock are in sync so what is the actual question? > > As I understand from your answer is by having configured ntp the hosts > > clock > > are in sync. > > we need to report that they are sync and how off the actual local clock is
once again, you have the solution so why ask the question? you assume ntpd - please make sure it is actually configured. > > Thanks, > michal > > >> > >>> > >>>> > >>>>> > >>>>> Thank you, > >>>>> Shahar Havivi. > >>>>> _______________________________________________ > >>>>> vdsm-devel mailing list > >>>>> vdsm-devel@lists.fedorahosted.org > >>>>> https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel > >>>>> > >>> > > _______________________________________________ > > vdsm-devel mailing list > > vdsm-devel@lists.fedorahosted.org > > https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel > > > > > > _______________________________________________ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
