In Disk to Disk to Tape, data is first copied from the backup server to hard disks. This technique for disk back ups used in Disk-to-Disk( D2D) is complemented by the subsequent backup to tape drives.
The advantage of the D2D2T technique is that the data exists for long-term archiving on magnetic tapes and simultaneously for several days as a backup on the hard disk. The slower access times of the tape devices complement the short access times of the hard disks. D2D2T systems can scale between several terabytes( TB) and several petabytes( PB) of storage capacity.