rpi ~$ time dd if=/dev/zero of=zerofile bs=4M
dd: error writing 'zerofile': No space left on device
434+0 records in
433+0 records out
1817587712 bytes (1.8 GB, 1.7 GiB) copied, 368.33 s, 4.9 MB/s

real    6m43.538s
user    0m0.002s
sys     0m15.563s

rpi ~$ rm zerofile
rpi ~$ sudo systemctl poweroff

laptop ~$ dd if=/dev/sdb bs=4M | gzip > backup.img.gz

laptop ~$ gzip -c backup.img.gz | dd of=/dev/sdb bs=4M conv=fsync