IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Communications Remarks
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instead of immediately. The integrity of such files can only be restored
using a generation dated earlier than the occurrence of the loss.
- It is always possible for data backups to be carried out incompletely or
incorrectly. In such cases, an additional generation often proves to be
useful.
For the generation principle to remain useful, a basic condition must be
fulfilled, i.e. the time interval between generations must not fall short of a
minimum value. Example: an automatic data backup process is disrupted
repeatedly; as a result, all existing generations are overwritten successively.
This is prevented by overwriting generations only after ensuring that their
minimum age has been maintained.
The generation principle is characterised by two values: the minimum age of
the oldest generation and the number of available generations. The following
applies here:
- The higher the minimum age of the oldest generation, the greater the
probability of the existence of a previous version of a file in which a loss of
integrity has occurred (including deleted files which would have proved
useful later).
- The greater the number of available generations, the higher the degree of
updating of the previous version.
However, the number of available generations is directly related to the costs of
data backup, as a sufficient number of data media must be available, too. This
is because every generation needs separate data media. For reasons of
economy, the number of generations must be restricted to an appropriate
value.
The parameters of the generation principle are selected in accordance with the
following standards:
Data availability and integrity requirements:
The higher the data availability or integrity requirements, the greater the
number of generations required to minimise the time needed to recover
from a loss of integrity. If file loss or integrity infringement can not be
detected until very late, additional quarterly or annual data backups are
recommended.
Reconstruction effort without data backup:
If the database is extensive but can be reconstructed without backups, it
can be considered as an additional "pseudo generation".
Data volumes:
The higher the volume of data, the higher the costs of maintaining a
generation, due to the increased storage requirement. High volumes of data
can therefore restrict the number of generations for reasons of economy.
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IT-Baseline Protection Manual: Oktober 2000