KVM: growing a ROOT volume through a new disk offering is refused while the VM is running, though a size-only resize of the same volume works #14601

ISSUE TYPE

• Bug Report

COMPONENT NAME

Volumes / resizeVolume / changeOfferingForVolume

CLOUDSTACK VERSION

4.22 (also main)

CONFIGURATION

KVM, any primary storage; seen on Ceph RBD.

SUMMARY

On KVM, a ROOT volume of a running VM can be grown in place: resizeVolume id=<root> size=<larger> goes through orchestrateResizeVolume, which explicitly handles a running KVM VM (it checks the host is Up and Enabled), and the agent grows the disk with virsh blockresize.

Growing the same volume by giving it a larger disk offering is refused, whether through resizeVolume id=<root> diskofferingid=<larger offering> or changeOfferingForVolume:

Cannot resize ROOT volume [ROOT-123] when VM is not on Stopped State. VM i-2-123-VM is in state Running

The refusal comes from VolumeApiServiceImpl.checkIfVolumeIsRootAndVmIsRunning, which runs only on the two disk-offering paths and refuses any size change of a ROOT volume unless the VM is Stopped, on every hypervisor. It dates from #4341, when ROOT volumes were first allowed to change disk offering at all; the size-only path never had this restriction on KVM.

So on KVM the same grow is accepted or refused depending on which API is used to request it. Where the ROOT volume's offering fixes its size, the size-only path is refused too (the volume "can only be resized when changing to another Service Offering"), which leaves stopping the VM as the only way to grow its root disk.

STEPS TO REPRODUCE

1. On KVM, deploy a VM; leave it Running.
2. resizeVolume id=<its ROOT volume> size=<current GiB + 10>
   -> succeeds; the guest sees the larger disk.
3. Create a disk offering larger than the volume, then:
   resizeVolume id=<its ROOT volume> diskofferingid=<that offering>
   (or changeOfferingForVolume id=<ROOT volume> diskofferingid=<that offering>)
   -> "Cannot resize ROOT volume [...] when VM is not on Stopped State"

EXPECTED RESULTS

On KVM, growing a running VM's ROOT volume through a new disk offering succeeds, as the size-only resize already does.
Shrinking a ROOT volume, and any ROOT resize on other hypervisors, still needs the VM to be stopped.

ACTUAL RESULTS

InvalidParameterValueException: Cannot resize ROOT volume [...] when VM is not on Stopped State.