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
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