Tape drives


Martin McBride, 2017-03-15
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Magnetic tape has been used is the past to store music (audio cassettes) and video (VCRs):

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These days they have mainly been replaced by optical discs and streaming. However, tape is still used by computers to store digital data. It works in a similar way to audio or video recording. The cassettes and recorders have a different design - they are more robust and reliable, but cost considerably more than typical VCR tapes and players.

Even so, they are still a relatively cheap way of storing very large amounts of data, in particular for backup purposes.

Characteristics

Tape storage:

  • is relatively cheap per byte.
  • has a reasonably fast rate of data transfer.
  • can store very large amounts of data.

A modern tape cartridge can store up to around 100 TBytes (100 x 1024 GBytes), which is considerably more than a hard drive, and far more than an optical disc. Cartridges are reasonably small and quite robust, so they are a very good way to store large amounts of data.

The main downside with tapes is that they only offer sequential access. It is quite fast to read or write data in one long, continuous stream. But if you want to jump around and read data from different places on the tape, it becomes very slow because you have to wait for the tape to wind to the correct place.

Tape backups

Many businesses perform daily backups of their systems, usually overnight when the office is closed. This may involve backing up everything on the file server. Tape is a good way to store these large backups.

It is quite common to have several tapes which are re-used. For example, an office might use 5 tapes (assuming they only backup on weekdays). A different tape is used each day, then after a week the oldest tape is erased and reused. This means that if, for example, an important file is deleted, it can be replaced from the backup, even if it was erased a few days ago and people have only just noticed.

For extra security, many businesses keep an off-site backup. This simply means storing the data at a different location. If the main office burns to the ground, or is burgled overnight, and everything is gone, there is still a copy of the data held safely in a different place. Tapes are ideal for this, as they are small, light and quite robust.

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