question about qemu-img convert

[Tapas Mishra]

I used following command
# qemu-img convert -c -f raw -O qcow2 /dev/nintendo/lvm1 /backup/lvm1.img
the /dev/nintendo/lvm1 is an LVM which is of 100Gb size.
It is taking really long time to do what I converted above.
My server does not have this much free space so that I can store one
100Gb image
The actual space occupied by /dev/nintendo/lvm1 is only  5GB or such that.
Will the above command create a new backup worth 100Gb.