# create/restore backup of disk
# remember: restoring can be done with a linux live image/usb
# bs=> OPTIONAL: block size of 4MB
# conv=sync,noerror => ignore read errors
# status=progress => display progress
sudo dd if=/dev/sda of=/var/tmp/backup.img status=progress conv=sync,noerror bs=4M

# restore backup of disk
sudo dd if=/var/tmp/backup.img of=/dev/sda status=progress conv=sync,noerror bs=4M

# backup with instant gzip
sudo dd if=/dev/sda status=progress conv=sync,noerror bs=4M | gzip -c  > /var/tmp/backup.img.gz
# restore with instant gunzip
sudo gunzip -c /var/tmp/backup.img.gz | dd of=/dev/sda status=progress