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Initiation responsibility: IT Security Management
Implementation responsibility: Administrator; staff responsible for the individual IT applications
The following influential factors must be determined for each IT system, possibly even for each individual IT application of particular significance. The system administrators and persons-in-charge of the various IT applications can be interviewed for this purpose. The results are to be comprehensibly documented.
The following theoretical example is to demonstrate how the influential factors can be determined in practice. This example involves a server-based LAN with 10 PC's connected as workstations. The IT system is used for processing orders with the help of a database. The application data are stored centrally on the network server.
The following individual items need to be established:
Specifying the data to be backed up
The data stock of the IT system (IT application) required to perform the specialised task must be determined. This includes the application and operational software, system data (e.g. initialisation files, macro definitions, configuration data, text blocks, password files, access-right files), the application data as such and the protocol data (log-ins, security violations, data transmissions).
Data availability requirements of the IT applications
The availability requirements for the data stated in the first step must now be stipulated. A proven standard here is the maximum permissible downtime (MPD). It specifies the time period during which the specialised task can be performed without the availability of these data and without the need for resorting to backup copies. Consideration must also be given as to whether paper usage would allow short- term continuation of operations without IT support.
Effort required for data reconstruction without data backup
To develop an economically efficient data backup policy, it is necessary to know whether, and how easily, destroyed databases could be reconstructed if backup data were not available. The sources from which the data could be reconstructed should be examined. Examples include documented files, printouts, microfiche, interviews and surveys.
The financial or operational effort required by a data registration crew should be calculated in terms of working days (WD).
Data volumes
A decisive factor in determining selection of the storage medium is the volume of data to be backed up. The required specification is based purely on the data to be backed up and is stated in megabytes (MB).
Modification volumes
To establish the frequency of data backup and an adequate backup procedure, the volume of data which is modified over a certain time period must be known. MB/week can conceivably be used as units here. Statements are also necessary as to whether the contents of existing files change or whether new files are generated .
Modification times
In some IT applications, data modifications take place only at certain times, e.g. bookkeeping at the end of the month. In such cases, data backup is only useful immediately after these points in time. For this reason, it should be specified as to whether the data to be backed up is modified daily, weekly or at other intervals.
Deadlines
It should be clarified as to whether certain deadlines must be observed for the data. This can involve storage or deletion deadlines relating to person-related data. These deadlines must be considered when laying down the data backup policy.
Confidentiality requirements
The confidentiality requirement of a file also applies to any backup copy. When adding backup copies with the same confidentiality requirement on to one data medium, this can result in an increased confidentiality requirement of the data stored. Consequently, specifications must be made as to the confidentiality requirements of the individual data blocks needing backup, as well as the data combinations which have a higher degree of confidentiality than the original data.
Integrity requirements
Data backups must ensure that data are stored integrally and not modified during the period of storage. The importance of this increases with the integrity requirements of the data in question. The integrity requirements of the data to be backed up must therefore be stated.
Knowledge and data-processing competence of IT users
To determine whether IT users, specially appointed employees or the system administrators are to carry out data backups, the knowledge and data processing capabilities of IT users as well as the tools available to them must be given primary consideration. If the time required by IT users for carrying out data backups is too long, this should be stated.
Additional controls:
| © Copyright
by Bundesamt für Sicherheit in der Informationstechnik |
July 1999 |