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" shaharh@redhat.com To: "Alon Bar-Lev" alonbl@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" shaharh@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
Thanks, michal
Thank you, Shahar Havivi. _______________________________________________ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
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