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On Wed, 2021-08-04 at 16:39 +0000, DHilsbos at performair.com wrote:
> All;
> 
> I had something unusual happen this morning; one of my VMs was showing "Suspended" under the Power State in the Horizon dashboard.
> 
> I've never seen that.  What does it mean?
> 
> Any search that I do points me to a bunch of resources for Status Suspended.
suspened is like hibernate in windows. in the libvirt driver we call libvirt managed_save api
this pauses the guests,  snapshots the guest ram and saves it to disk then stops the instance.
so this frees the guest ram on the host and save it to a file so that we can recreate the vm and resume it
as if nothing happened.

nova also supports pause.
pause is similar to suspend but much less invasive.
pause jsut stops the execution of the guest cpus but the guest qemu process is still running.


if you have pci passtough device when you use suspend the device are detach before its suspended 
 and then reattached when its resumed.

if you use pause we dont need to do this since the dma regoins for the passthough devices are never touched.

different virt dirver may or may not supprot pause/suspend and they may work differently.

suspeedn is bascally supend the guest execution to disk where as pause is like you laptos sleep or suspend to ram.

in a could env i dont really think either are that useful if im being honest and im not sure we woudl add them today if
they did not really exits,

generally if the vm is not running you should shleve it.

from a schduler point of view pausign, suspending and stoping an insntce all use the same amount of resouces as a runnign instnace
so form a billing perpsective public cloud will change you the same for all 4 states.

shelve instance are only using disk space and floating ips so genrealy that will be reflected  in the cost and it will be much cheaper on
a public cloud to shelve an instnace.


> 
> Thank you,
> 
> Dominic L. Hilsbos, MBA
> Vice President - Information Technology
> Perform Air International Inc.
> DHilsbos at PerformAir.com
> www.PerformAir.com
> 
>