All of them have a `+size` prefix to show that they're not
"pure raw" or "pure tar" streams, because some storage may
need to know in advance how much storage to allocate.
The formats are explained in comments.
PVE::Storage::Plugin now has default implementations for
these for non-incremental streams exporting the current
(rather than a snapshot state).
To use qcow2 or vmdk formats $with_snapshots must be true,
otherwise raw/tar will be used where $with_snapshots must
be false.
This deletes a snapshot on *success*, done directly in the
CLI handler, as the rollback/delete on failure is already
happening inside the plugin's import method.
It is possible to synchronise a volume to an other node in a defined interval.
So if a node fail there will be an copy of the volumes from a VM
on an other node.
With this copy it is possible to start the VM on this node.
