Traditional backup is generally performed using a tape based backup system with software providing the control. Whilst there have been significant advancements in tape technology over the years it is still a relatively slow process and has particular weaknesses when it comes to useful life of the tapes, time taken to backup and restore and the integrity of the data.
Backing up a large system can be slow using tape backup, as data is stored sequentially along the length of the tape. This means that if you need to restore a document that has been saved at the end of the tape you need to wind the tape forward to the relevant point before being able to restore the file. On large systems this can take over half an hour to an hour to complete.
To try and speed up tape backup, systems managers use various techniques such as the incremental backup method to back up their systems. Incremental backup means that only files that have changed since the last backup are backed up to tape thereby reducing the amount of data transferred to tape.
This reduces the time taken to backup, however if things go wrong and you need to restore, then the user must go back to the last ‘full’ backup and re-install all of the incremental tapes in order. This can be very time consuming assuming all of the tapes are available and can be re-read and be restored. So backing up can be speeded up on tapes but restoring can take quite a while.