Versioning and parameters
TSM provides both an automatic as well as a user-initiated backup of data. As far as possible the automatic backup should be used in order to ensure a regular backup.
The entire control system and communication between client and server is provided by the corresponding TSM software modules. The files to be backed up or restored are thereby transferred between TSM client and TSM server via the network.
The backup with TSM is in clear contrast to other back up products. TSM provides a backup on the file level. Each file is managed as an individual object on the TSM server. Consequently it is possible, with each backup, to only transfer the changes in the client system's file system onto the TSM server.
While a regular incremental backup only saves all those files in a bundle, that were modified or newly created since the last backup, the TSM also informs the server, which files were deleted since the last backup.
Naturally, each new file is also saved as an independend object on the TSM server.
Versioning of Data
The TSM server uses information that are transferred during the incremental backup in order to update the status of the backup copy. If e.g. a file is identified as deleted, it will be retained from that moment on for a pre-set time period (as inactive version) and subsequently deleted on the server as well. To control which versions of a file are retained for how long, four parameters are configured on the server:
- Versions Data exists indicates how many different versions of a file are maximally backed up on the TSM server. If the indicated number is exceeded by a new backup the oldest version is directly deleted during the backup.
- Versions Data deleted indicates how many different versions of a file are backed up on the TSM server if the file is locally deleted. If the file is locally deleted the oldest redundant versions of the file are also deleted on the server.
- Retain extra Versions indicates for how many days the versions of a file (except for the latest) that are still available after the evaluation of "Versions Data deleted" are backed up on the server after the file is locally deleted. If the file is still available locally, "Retain extra versions" indicates for how long the older versions of a file are maximally retained, provided the number given by "Versions Data exists" is not exceeded.
- Retain only Version indicates for how many days the last version of a file is backed up on the server after the file was locally deleted.
Example for the versioning of files
This example illustrates the versioning of a file within the TSM server. The following paramters are defined:
|Versions Data exists||3|
|Versions Data deleted||2|
|Retain extra Versions||7|
|Retain only Version||14|
|O||Active Version of the File.|
|-||Inactive Version of the File.|
|X||Last version of the deleted file.|
|A||This version will be deleted since the seven days (Retain extra versions) expired.|
|B||The oldest version will be deleted since the number of three versions (Versions Data exists) was exceeded.|
|C||Version will be deleted since the file was deleted and therefore only two versions (Versions Data deleted) are retained.|
|D||The last version of a file will be deleted after the expiry of 14 days (Retain only Version).|
The parameters were especially selected for the example in order to further clarify their functionality of the versioning. The values used here are not available as a parameter set for the backup at the IT Center. The current settings of the server can be detected with the TSM client via the View Policy Information in the menu "Utilities" at all times.
Currently at least the following paramters apply in the default management class:
|Versions Data exists||5|
|Versions Data deleted||4|
|Retain extra Versions||30|
|Retain only Version||183|
Please note that these parameters can be modified by the IT Center. The currently valid settings can at all times be requested via the TSM client (see above).