I wish to run 2 copies of an application that need to communicate. They will be on DomUs on different machines. The application needs the DomUs to be in very close time sync. On the metal I would just set each machine up as a stratum 3 ntp server. I believe that in Xen the DomU picks up the time from the Dom0 and it is a bad idea to use date/ntpdate on the DomU. This leads to 2 questions. 1) I changed the time on the Dom0s but the DomUs didn''t pick up the change, can I force the DomUs to update their clocks or do I need to restart them? 2) what is the advisability of running the Dom0 as a ntp stratum 3 server? I know that you should run the minimum possible on the Dom0 Thanks for all advice John -- John Landamore Department of Computer Science University of Leicester University Road, LEICESTER, LE1 7RH J.Landamore@mcs.le.ac.uk Phone: +44 (0)116 2523410 Fax: +44 (0)116 2523604
J. Landamore wrote:> I wish to run 2 copies of an application that need to communicate. They > will be on DomUs on different machines. The application needs the DomUs to > be in very close time sync. On the metal I would just set each machine > up as a stratum 3 ntp server. > > I believe that in Xen the DomU picks up the time from the Dom0 and it is a > bad idea to use date/ntpdate on the DomU. This leads to 2 questions. > > 1) I changed the time on the Dom0s but the DomUs didn''t pick up the > change, can I force the DomUs to update their clocks or do I need to > restart them? >From this thread - http://opensolaris.org/jive/thread.jspa?messageID=263362 Stuart Maybee states - "The dom0 does not keep time for the domU''s nor does it hand time to them. The hypervisor provides the time to all domains. It retrieves it from the physical hardware. DomU''s get their time from the hardware emulation provided by the hypervisor. The only interaction dom0 has is that it has the capability of setting the hardware time. Solaris will attempt to set the hardware time to UTC based on the time zone it is configured in. But if you for instance set the time in dom0 to a different time after you started domU''s then I doubt the domU''s would see the changed time. (e.g if you set dom0 to a different timezone after the domU''s were started) ..." In light of this, I think the easiest solution would be to run ntpdate periodically in each domU.> 2) what is the advisability of running the Dom0 as a ntp stratum 3 server? > I know that you should run the minimum possible on the Dom0 >ntp stratum server doesn''t sound like its going to make heavy demand of computing resources. I don''t wouldn''t think it would over-burden a dom0. --joe