XenServer has the ability to pause an instance that will also preserve the instance's memory state. Un-pause, of course, should also be available. This is an admin-only operation.
Some interesting issues with mapping power-states. The difference between xs-pause and xs-suspend is how memory is persisted (suspend -> disk, pause -> memory)
We'll do the same thing. This implies that there will not be an implicit "suspended" state in nova.compute.
* Blueprints in grey have been implemented.