[Users] Time keeping in Windows VM
m.j.goldstone at keele.ac.uk
Tue Nov 19 16:36:24 UTC 2013
We're currently experiencing an issue in our production oVirt 3.2.2
environment (on CentOS 6.4) with time keeping on our Windows guests. It
seems to have appeared around the time of the recent DST change. It's taken
us a while to get to the bottom of this as some machines were created in
the wrong timezone, which muddied the waters a bit.
It appears that when Windows automatically updated time in the VMs, this
new offset from UTC was not stored correctly, and the next time the host
was shutdown and started back up, the clock was set incorrectly. We
eventually managed to get this to be consistently reproducible: Set the
clock an hour ahead; power off VM; power it back on; set the clock an hour
back (ie return it to the original time), power off and power back on;
observe that the clock has now shifted to an hour before the original time.
This can be observed in the vm_dynamic table on the database.
To be honest, I don't think that this an oVirt problem, as I've done some
limited testing on another host using virt-manager/libvirt. If I edit the
xml to set the clock offset to variable, using UTC as the basis and setting
the adjustment to 3600 (mimicking how it would have been before the DST
change), when I change the time in the VM back by an hour (as Windows would
do automatically at DST change), the xml shows a new offset of -3600, so it
seems when the clock is changed the offset it's putting in the XML is the
offset based on the time from when the VM was started, not the offset from
Does anyone have any suggestions? At the moment, the only things I can
think of doing are either a) shutting down each VM and setting their offset
to 0 in the vm_dynamic table before starting the back up again or b)
setting the time forward and back an appropriate amount of time so that the
offset becomes 0, shutting the VM down and powering it back on again.
IT Systems Administrator - Finance & IT
Keele University, Keele, Staffordshire, United Kingdom, ST5 5BG
Telephone: +44 1782 734457
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