IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Communications Remarks
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Incremental data backups are always based on full data backups and should
be interspersed periodically by full data backups. During restoration, the
last full backup is taken as a basis which is then extended with the updates
from subsequent, incremental backups.
- Differential data backup: This procedure stores only the files that have
been changed since the last full data backup. A differential backup requires
more memory space than an incremental backup but the files can be
restored quicker and easier. For restoration of data, the last full data backup
will suffice as will the most recent differential backup. This is not the case
with an incremental backup, since under some circumstances many data
backups must be read one after the other.
A special form of the above-mentioned data backup strategies is image
backup. This procedure backs up the physical sectors of the hard disk instead
of the individual files on it. This is a full backup which allows very quick
restoration on hard disks of the same type.
Another form of backup is Hierarchic Storage Management (HSM). This
primarily involves the profitable utilisation of expensive data media.
Depending on the frequency at which they are accessed, files are stored on fast
on-line media (hard disks), near-line media (automatic data- media changing
systems) or off-line media (magnetic tape). Generally, these HSM systems
also allow a combination of incremental and full data backup.
Redundant data storage is allowed by RAID (Redundant Array of Inexpensive
Disks) systems. The RAID concept represents the linkage of several hard
disks under the command of an array controller. There are various RAID
levels, RAID level 1 involving data mirroring.
RAID systems are no replacement for data backups! The do not offer
assistance in case of theft or fire. The data stores on RAID systems therefore
has to be stored on additional media which have to be sited in different fire
lobbies.
To select a suitable and economically efficient data backup strategy, the
following factors should be taken into account:
Availability requirements:
If availability requirements are extremely high, data mirroring should be
considered. If availability requirements are high, full data backup is
preferable to incremental data backup.
Data and modification volumes:
If the modification volume is similar to the data volume (e.g. in the use of a
database), the storage capacity saved by incremental data backup is so
negligible that full backup should be considered. However, if the
modification volume is much smaller than the data volume, the storage
capacity saved by incremental data backup is considerable and reduces
costs to a large extent.
Data modification times:
Data modification times can have a minor influence on the data backup
strategy. If an application requires backup of the entire database at certain
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IT-Baseline Protection Manual: Oktober 2000