bmaptool(1), from the bmap-tools package, can write the used blocks
in a sparse disk image to media, while saving time and I/O by not writing
zeroes to the unused blocks. Typical use:
make raspi2_bullseye.img.bmap raspi2_bullseye.img.xz
... upload those two files ...
... download those two files ...
bmaptool copy raspi2_bullseye.img.xz /dev/disk/by-id/usb-Generic-_SD_MMC_*-0:0
Signed-off-by: Simon McVittie <smcv@debian.org>