The guest fs is created in the qcow when you installed the guest. So your qcow is a complete disk including MBR, filesystem tables, journaling,….
dd is a classic linux command: please read ‘man dd’ (to be less polite, RTFM: don’t use commands until you have at least read the man page…)
quick usage: dd if=image.raw of=/dev/lv-group/volume bs=4M
The logical volume can be seen as a real disk-partition… Like this your guest is (almost) directly reading and writing to the host disk. That’s why this setup is so fast.
Make sure the logical volume is at least equal size as the raw image!!! If it is not, the volume will be corrupted. I always work in bytes and not in Gb to prevent mistakenly switching gigabytes and gibibytes…
It’s not a problem if the logical volume is larger then the raw (not good practise but like this you’re on the safe side until you’re really familiar with lvm…)
the command dd will write the content of the raw, byte for byte, to the logical volume. So, it’s like mirroring the volume offline…
Change the guest disk(s) to use the logical volume (I do this with virt-manager: remove the volume without erasing the image, and recreate using the logical volume)
Then rename the qcow to qcow.old or something, so you’re sure you’re using the logical volume and not by accident still the qcow
I know it’s a hand full but once you’re familiar with it, you can do really cool stuff with lvm…