This article how strategy shapes structure pdf about backup in computer systems. Backups have two distinct purposes.
Organizing this storage space and managing the backup process can be a complicated undertaking. A data repository model may be used to provide structure to the storage. Before data are sent to their storage locations, they are selected, extracted, and manipulated. Many different techniques have been developed to optimize the backup procedure. It is important to recognize the limitations and human factors involved in any backup scheme. Any backup strategy starts with a concept of a data repository.
The backup data needs to be stored, and probably should be organized to a degree. A more sophisticated setup could include a computerized index, catalog, or relational database. Different approaches have different advantages. An unstructured repository may simply be a stack of or CD-Rs or DVD-Rs with minimal information about what was backed up and when.
This is the easiest to implement, but probably the least likely to achieve a high level of recoverability as it lacks automation. A repository of this type contains complete system images taken at one or more specific points in time. This technology is frequently used by computer technicians to record known good configurations. An incremental style repository aims to make it more feasible to store backups from more points in time by organizing the data into increments of change between points in time. This eliminates the need to store duplicate copies of unchanged data: with full backups a lot of the data will be unchanged from what has been backed up previously.
Restoring the whole system to the date of the last incremental backup would require starting from the last full backup taken before the data loss, and then applying in turn each of the incremental backups since then. Additionally, some backup systems can reorganize the repository to synthesize full backups from a series of incrementals. Each differential backup saves the data that has changed since the last full backup. It has the advantage that only a maximum of two data sets are needed to restore the data. Restoring an entire system would require starting from the most recent full backup and then applying just the last differential backup since the last full backup. Note: Vendors have standardized on the meaning of the terms “incremental backup” and “differential backup”.