Maybe qm snapshot does what you want. Have a look at the manpage:
Code:
qm snapshot <vmid> <snapname> [OPTIONS]
Snapshot a VM.
<vmid>: <integer> (1 - N)
The (unique) ID of the VM.
<snapname>: <string>
The name of the snapshot.
--description <string>
A textual description or comment.
--vmstate <boolean>
Save the vmstate