[ironic] Each deploy overwrites the entire target disk

Dears, I have a question regarding the default behaviour of Ironic Python Agent - it seems that each deploy causes the entire target disk to be overwritten. I have noticed this after replacing disks with larger ones, the deployment process started taking considerably longer and I observed that each sector is rewritten on the target device. Is that expected? Can I somehow avoid it? I am using whole-disk, qcow2 images that are much smaller than the disk size (even in raw form). I am running Ironic Wallaby. The deployment method is direct. Kind regards, -yoctozepto