Open Stack

  Greetings,

A blueprint is being discussed about the disk resize down feature of libvirt driver.
  https://blueprints.launchpad.net/nova/+spec/libvirt-resize-disk-down

The current implementation does not handle disk resize down and just skips the
step during a resize down of the instance. I'm really convinced we can implement 
this feature by using the good job of disk resize down of the driver xenapi.

Criteria for allowing disk resize down:
  + The disk must have one partition
  + The fs must be ext3 or ext4

The implementation will be separated in several commits:
  + Move shared utility methods to a common module:
    - virt.xenapi.vm_utils._get_partitions to virt.disk.utils.get_partitions
    - virt.libvirt.utils.copy_image to virt.disk.utils.copy_image
    - virt.xenapi.vm_utils._repair_filesystem to virt.disk.utils.repair_filesystem
  + Disk resize down implementation

Notes:
  - Another point we have to discuss, is that the current implementation just skips
    the fs resize if not supported, is it a good choice? Should we have
    to raise an exception to inform the user that it is not possible to resize
    the instance? (if we have to raise an exception, a task will be added to the
    TODO to handle this case for resize up before working on resize down.)
  - The current workflow for a user is to confirm the resize when the state
    of the instance is VERIFY_RESIZE, I think we probably have to add a
    checklist of good pratices of how to verify a resize in the manual:
      http://docs.openstack.org/user-guide/content/nova_cli_resize.html

Thanks a lot,
s.