The term "disk-to-disk" or "D2D" is typically used in reference to disk-to-disk backup. Disk-to-disk backup allows a computer's hard drive to be backed up and restored to a different hard drive, instead of using a tape or floppy disk.
Two of the biggest advantages of using disk-to-disk backup are the higher speed and capacity offered by hard drives in comparison to tapes or floppy disks, which allows for shorter backup and recovery times. Disk-to-disk also allows for non-linear recovery of data, meaning a specific file can be restored more quickly and simply compared to tape.
Remote backup services exist allowing users to backup files using disk-to-disk while the data is stored in a remote location usually provided by managed backup providers.