'qemu-img create' to backup encrypted qcow2 - ?

[lejeczek]

Hi guys.

I am trying to backup qcow2s which are luks encrypted but I 
fail and I wonder if it's my syntax being crooked or 
something is not working in qemu(-img).
Non-encrypted qcow2 works fine and I only add encryption 
bits to cmd line, here:

-> $ qemu-img create -f qcow2 -b -o 
encrypt.key-secret=3fd57349-3671-4cf2-ab00-f13b8ba00a4d 
/00.GLUSTER-mnt/VMs3/enc.locallan.qcow2 -F qcow2 
./enc.locallan.qcow2.bkp
qemu-img: Invalid image size specified. You may use k, M, G, 
T, P or E suffixes for
qemu-img: kilobytes, megabytes, gigabytes, terabytes, 
petabytes and exabytes.

Care to share your thoughts I'll appreciate.
many thanks, L.