Date: Tue, 03 Nov 2015 19:15:41 +0100 From: Karl Pielorz <kpielorz_lst@tdx.co.uk> To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= <roger.pau@citrix.com>, freebsd-xen@freebsd.org Subject: Re: 'Live' Migrate messes up NTP on FreeBSD domU - any suggestions? Message-ID: <EA864F2D8721BF82F5892B06@Mac-mini.local> In-Reply-To: <563898B0.5040100@citrix.com> References: <151F73F1EF071C3C48F17866@[10.12.30.106]> <5637A01B.1010307@citrix.com> <8448B4CE863936ADEF762C0F@[10.12.30.106]> <563898B0.5040100@citrix.com>
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--On 3 November 2015 at 12:21:20 +0100 Roger Pau Monn=C3=A9=20 <roger.pau@citrix.com> wrote: > Can't you tell ntpd to just resynchronize no matter what skew it detects? Probably - I'll have to do some digging - I had hoped someone had hit this=20 already, though I'm also a little concerned about throwing a 7 second 'back = in time' jump on the system. >> Are either of those fixes likely to cure this? > > Hm, I don't think so. Both commits are present from 4.3 onwards, and > IIRC XenServer 6.5 is based on Xen 4.4, which should contain both fixes. > > Is XenServer also synchronized using ntpd? When a guest resumes from > migration is updates it's current time based on the time provided by the > hypervisor, so if the hosts themselves are not synchronized you could > see skews like that. All the clocks on the XenServers are NTP sync'd - and are in sync=20 (confirmed from the consoles). When the domU moves - it's clock moves >ahead< in time of both the server=20 it's leaving, and the server it's moved to. I re-ran the test adding checks for the source (Xen1) and destination=20 (Xen2) XenServer clocks - and I get: Me: Tue Nov 3 18:56:29 GMT 2015 Them: Tue Nov 3 18:56:29 GMT 2015 Xen1: Tue Nov 3 18:56:29 GMT 2015 Xen2: Tue Nov 3 18:56:29 GMT 2015 (All in sync) [moving FreeBSD from Xen1 to Xen2] Me: Tue Nov 3 18:56:39 GMT 2015 (Gained 4 seconds) Them: Tue Nov 3 18:56:35 GMT 2015 Xen1: Tue Nov 3 18:56:35 GMT 2015 Xen2: Tue Nov 3 18:56:35 GMT 2015 Me: Tue Nov 3 18:56:43 GMT 2015 (Completed - gained 7 seconds total) Them: Tue Nov 3 18:56:36 GMT 2015 Xen1: Tue Nov 3 18:56:36 GMT 2015 Xen2: Tue Nov 3 18:56:36 GMT 2015 Me: Tue Nov 3 18:56:44 GMT 2015 Them: Tue Nov 3 18:56:37 GMT 2015 Xen1: Tue Nov 3 18:56:37 GMT 2015 Xen2: Tue Nov 3 18:56:37 GMT 2015 So you can see it's now 7 seconds ahead of both 'Them' (external bare metal = machine running ntp) and Xen1/Xen2. I re-ran the test without ntp loaded on the domU - and the same thing=20 happens - so it's not ntp causing it. We've kind of 'lived with it' until now - but as the quantity of VM's=20 increases - it becomes more of a pain :( -Karl
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