5.1. Reasons for Backup and Restore
Backup is performed for various reasons, and those reasons very often dictate the investment made in accomplishing the backup. The assurance of data availability is the primary reason for creating backups. The higher the data availability requirements, the more investment needs to be made. For example, one form of backup that runs continuously is disk mirroring, in which every data write operation is reflected to another disk to guarantee extremely high data availability.
Data archival also is used to meet legal and other needs in which the data does not have to be accessible immediately but can be produced on demand in a reasonable amount of time, measured in hours, days, or weeks.
Backups are sometimes used ...