Disk staging is using disks

Hard disk

A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...

 as an additional, temporary stage of backup

Backup

In information technology, a backup or the process of backing up is making copies of data which may be used to restore the original after a data loss event. The verb form is back up in two words, whereas the noun is backup....

 process before finally storing backup to tape

Magnetic tape data storage

Magnetic tape data storage uses digital recording on to magnetic tape to store digital information. Modern magnetic tape is most commonly packaged in cartridges and cassettes. The device that performs actual writing or reading of data is a tape drive...

. Backups stay on disk typically for a day or a week, before being copied to tape in a background process and deleted afterwards.

The process of disk staging is controlled by the same software that performs actual backups, which is different from virtual tape library

Virtual Tape Library

A virtual tape library is a data storage virtualization technology used typically for backup and recovery purposes. A VTL presents a storage component as tape libraries or tape drives for use with existing backup software.Virtualizing the disk storage as tape allows integration of VTLs with...

 where intermediate disk usage is hidden from main backup software. Both techniques are known as D2D2T (disk-to-disk-to-tape).

Restoring data

Data is restored from disk if possible. But if the data exists only on tape it is restored directly (no backward-staging on restore).

Reasons

Reasons behind using D2D2T:

• increase performance of small, random-access restores: disk has much faster random access than tape
• increase overall backup/restore performance: although disk and a tape have similar streaming throughput, you can easily scale disk throughput by the means of striping
  Data striping
  In computer data storage, data striping is the technique of segmenting logically sequential data, such as a file, in a way that accesses of sequential segments are made to different physical storage devices. Striping is useful when a processing device requests access to data more quickly than a...
  
   (and tape-striping is a much less established technique)
• increase utilization of tape drive
  Tape drive
  A tape drive is a data storage device that reads and performs digital recording, writes data on a magnetic tape. Magnetic tape data storage is typically used for offline, archival data storage. Tape media generally has a favorable unit cost and long archival stability.A tape drive provides...
  
  s: tape shoe-shining effect is eliminated when staging (note that it may still happen on tape restores)