[CentOS-virt] Time

Wed Jan 2 13:31:47 UTC 2013
SilverTip257 <silvertip257 at gmail.com>

On Wed, Jan 2, 2013 at 3:53 AM, Robert Dinse <nanook at eskimo.com> wrote:

>      Friday, I moved our servers to a new co-lo facility and ran into an
> interesting problem with virtual machines.
>      I did an orderly shutdown of the CentOS 6.3 host, and it in turn
> suspends
> all the guests.  It took about an hour and a half to move and fire up the
> host.
By default VMs suspend when the host node is shutdown.  You can change this
behavior in /etc/sysconfig/libvirt-guests

By shutting down the VMs you don't have to wait for the in-memory data to
be dumped to disk, nor do you have to wait for it to be copied back from
disk and into memory on boot.

>      The guests, being suspended, were then an hour and a half behind and
> it
> seems ntpd does not want to correct more than 1000 seconds of error so it
> would
> not automatically adjust the clocks.

At my place of employment we noticed the same thing during maintenance, the
VMs had their clocks all out of whack.

>      I tried the -g argument which is supposed to override the 1000 second
> limit but it did not.  I ended up having to manually set the clocks close
> enough for ntpd to correct.
I believe we had manually correct the clocks as well on ours, but it's been
months since then.

>      Since there is no hardware clock for the virtual machines to use when
> they
> boot, it seems that shutdown and reboot of the virtual machines probably
> would
> not have avoided this.
>      Any suggestions for addressing this particular scenerio other than
> having
> to manually set a bunch of clocks?
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//  SilverTip257  //
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