8.2.5. Storage of Backups
Once the backups are complete, what happens then? The obvious answer is that the backups must be stored. However, what is not so obvious is exactly what should be stored -- and where.
To answer these questions, we must first consider under what circumstances the backups are to be used. There are three main situations:
- Small, ad-hoc restoration requests from users
- Massive restorations to recover from a disaster
- Archival storage unlikely to ever be used again
Unfortunately, there are irreconcilable differences between numbers 1 and 2. When a user accidentally deletes a file, they would like it back immediately. This implies that the backup media is no more than a few steps away from the system to which the data is to be restored.
In the case of a disaster that necessitates a complete restoration of one or more computers in your data center, if the disaster was physical in nature, whatever it was that destroyed your computers would also have destroyed the backups sitting a few steps away from the computers. This would be a very bad state of affairs.
Archival storage is less controversial; since the chances that it will ever be used for any purpose are rather low, if the backup media was located miles away from the data center there would be no real problem.
The approaches taken to resolve these differences vary according to the needs of the organization involved. One possible approach is to store several days worth of backups on-site; these backups are then taken to more secure off-site storage when newer daily backups are created.
Another approach would be to maintain two different pools of media:
- A data center pool used strictly for ad-hoc restoration requests
- An off-site pool used for off-site storage and disaster recovery
Of course, having two pools implies the need to run all backups twice or to make a copy of the backups. This can be done, but double backups can take too long, and copying requires multiple backup drives to process the copies (and probably a dedicated system to actually perform the copy).
The challenge for a system administrator is to strike a balance that adequately meets everyone's needs, while ensuring that the backups are available for the worst of situations.