There are two primary objectives for performing backups. The first is to protect the system state. This involves a complete, sector by sector image of the complete hard drive. This needs to be done every time your system changes in some major way, typically new software installations or updates.
The second is for the preservation of data. An individual application or even an entire operating system can be recovered by reinstalling the original software and performing necessary updates, but if the data is lost, without some form of backup, it is simply lost. Some forms of data can be quite difficult, if not impossible to recover.
Backup procedures should establish who has accountability for making backups and define the frequency in which backups are performed.
There are three different approaches for performing acceptable data backups:
- Full backup - All data is backed up, and takes the longest to perform. The archive bit is cleared. Last full backup is the only requirement for a restore procedure.
- Differential backup - All data since the last full backup is backed up. The archive bit is not cleared. The last full backup plus the last differential backup are both required for a restore procedure.
- Incremental backup - Only files that have changed since the last backup are backed up. The archive bit is cleared. The last full backup plus all incremental backups performed since the last full backup are required to perform a restore procedure.