You can make a backup of a drive using dd
dd if=/dev/sda of=myfile.img
then restore it later
dd if=myfile.img of=/dev/sda
or over the network
dd if=/dev/sda | pv --size XXg | gzip --best | ssh user@ip 'dd of=/mnt/backups/sda.img'
You can determine the size of a hard drive with
fdisk -l /dev/sda