dd if=/dev/mmcblk0 of=$HOME/backup.img
dd if=/dev/mmcblk0 bs=64K conv=noerror,sync status=progress | gzip -c > /mnt/tbcrypt/lego.img.gz- bs=BYTES
- read and write up to BYTES bytes at a time (default: 512); overrides ibs and obs
- conv=CONVS
- convert the file as per the comma separated symbol list
- fdatasync
- physically write output file data before finishing
- fsync
- likewise, but also write metadata
- Source: Full Metal Backup Using the dd Command - Linux.com