dd command examples

use dd to create file of any size
dd if=/dev/zero of=testfile_10MB bs=10485760 count=1

Backup Entire Harddisk to an Image
Backup content of the harddrive to a file. Creates an image of the drive
dd if=/dev/sda of=/tmp/sda.iso


back hard disk to remote host
dd bs=1M if=/dev/hda | gzip | ssh user@ip_addr 'dd of=hda.gz'