Hi,
so we played around with Windows on OpenNebula a little more.
One thing that stood out was that if you suspend and resume a VM the hardware clock isn’t updated for the resume, and even with the guest agent installed, nothing fixes the clock, it’ll be still at the time of shutdown.
I think that’s not OK. I mean… _of course it’s not OK 
Imagine that happening inside a database cluster…
if you’re not at some startup where you can brag about how you found the error, then you’ll be glad if you just get fired over it!
So, I tried to see how to solve it… I searched for a few hours and so far I found out those things:
The libvirt way, and a Hook script
There’s a virsh command to “buff” the clock:
virsh domtime one-vmid --now
I’ll be honest and mention my libvirt doesn’t even have that flag 
One person has apparently made a hook for this:
what time is it anyway?
There’s a KVM setting "localtime"
That means the HW clock will not be a UTC clock I think. Windows would like that, but it is not a default.
Supported since http://dev.opennebula.org/issues/2547
anyone need some more settings?
This can be expanded further with other parameters:
clock offset=‘localtime’>
timer name=‘rtc’ tickpolicy=‘catchup’/>
timer name=‘pit’ tickpolicy=‘delay’/>
timer name=‘hpet’ present=‘no’/>
/clock>
(I had to remove the opening braces since forum always tried to parse the XML…
###Features
This would be incompatible with the FEATURE flag and mean one needs to put it in the raw section.
I think “catchup” could be interesting.
Other thing people have tried is using cron / scheduler etc. to ntp sync their clocks. That’s kinda shitty and nothing I want to do on servers, unless there’s really no other way in the universe.
##So, please, tell me:
- Did you fix this?
- How did you fix this
- Which approach is best for you?
- Any comment about how the hook does it?
Side note
For Linux, as far as I could see it’s all fine IF, and only IF, you use the KVM clocksource, kvm-clock.
As a Xen user (at heart, not in this setup) I know that having a proper paravirtualized clock is utterly important for scalability. I checked my VMs for that, and it’s fine:
cat /sys/devices/system/clocksource/clocksource0/current_clocksource
kvm-clock