Setting up a redundant architecture ensures that system data will be available but does not protect the data against user-introduced errors or against natural disasters such as fires, floods or even earthquakes.
Therefore it is necessary to set up backup mechanisms (ideally remote) in order to guarantee data perenniality.
Moreover, a backup mechanism can also be used for archival storage, i.e. saving data in a state that corresponds to a given date.
Types of Backup
No matter what damage takes place, the implemented backup mechanism absolutely must be designed to ensure the perenniality and recovery of all of a company's critical data without disrupting the running of the computer system. Therefore, choosing a backup mechanism must be the subject of a backup strategy that defines the data to be backed up, the backup frequency and method, and a disaster recovery plan that indicates the steps necessary for reestablishing normal functioning in case of a problem.
Backups are generally divided into the following categories.
- Full backup
- Differential backup
- Incremental backup
- Delta backup
The goal of full backup is to make a true copy of the data to be backed up on a separate medium. And yet, for large volumes of data, full backup can be slow (if the data are modified during backup) and can cause availability problems because it creates long and intense and even expensive access disks, given the capacity that is necessary. On the other hand, full backup provides a reliable image of the data in time t.
Incremental backup consists of copying all the elements that have been modified since the previous backup. This type of backup is more effective than a full backup because it focuses specifically on the modified files with a weaker storage space but, on the other hand, requires having previous backups in order to restore the full backup.
Differential backup focuses specifically on the files that have been modified since the last full backup, which makes this backup slower and more expensive in storage space than an incremental backup but also more reliable because on the full backup is needed to restore the backed up data.
Delta backup is an incremental backup of data elements with a fine data granularity, i.e. blocks of data are saved rather than individual files.