Disk-based backup solutions are ideal for daily data backup, as hard disks have significant speed advantages over tape. For disk backups, there are several combined approaches where the backups reside on hard disks and magnetic tape drives.
A simple disk backup is Disk to Disk( D2D), which is characterized by its high speed. The backup is done from the hard disk to a backup hard disk. A cost-effective long-term storage offers Disk to Disk to Tape( D2D2T). Here, the backup is transferred from the backup hard disk to a tape drive, tape backup. A backup technique with two tape backups is Disk to Tape to Tape( D2T2T), and the backup technique working with a cloud is Disk to Disk to Cloud( D2D2C).
Since the backup-to-disk approaches involve integrating the disk into the file system, the approach is usually inefficient due to the overhead. Therefore, alternative solutions include approaches in which the disk backup systems emulate virtual tape libraries.