Compression

By selecting "Compression" a compression program (packer) can be activated to compress the data in the backup. The packer compresses all data read and sends it to the selected target drive (destination).

The usage of compression software depends on several different factors:

The amount of space saved depends on the kind of sata saved. That means that more data can be saved to the target drive; possibly more than one backup can be stored to the same destination media. Text files, emails, etc. produce a relatively high compression ratio (>50%) while sound files produce a relatively low ratio. The type of compression algorithm effects the compression ratio as well. Some algorithms are optimized for compressing certain kinds of data (sound data or picture data).
Compression programs require more attention from system resources. The time necessary depends on the packer used, although all packers generally increase backup time or decrease writing speed.
If the destination supports hardware compression (e.g. SCSI streamer), the software compression isn't needed. Hardware compression is always faster and better than software compression. If hardware and software compression are both activated the result won't be a doubled pack ratio. If compressed software data will be sent to a hardware compression destination it will slow down the drive and the hardware compression will possibly expand the data.
Data safety, an important part of a backup. Repeatly used backup media can accumulate errors through the passage of time. Restoring compressed data from a media containing errors can be a large problem. In most cases it isn't possible to decompress defective data. Siegfried Backup minize this problem by compressing each file for individually. Because of this only files in defective sectors can be lost and not the whole backup!

Siegfried Backup can be dynamically extended with new packers. Add-ons are used to reach this goal. For every kind of compression an add-on can be created. An add-on is similar to an external library of program code to control the respective compression routines.

To add a new compression add-on file to Siegfried Backup, simply copy the file in the folder "Backup/Backup_Server/add-on/compressors". The following add-on's are available at this time:

Name File Comment
None SFNone That's only a dummy. 'None' does no compression. It only copies the data. 'None' should be used if compression is turned off (default).
LZRW1 SFLZRW1 Packer that uses the LZRW algorithm. That is a fast compression with an average pack ratio (mostly 40%).

To choose the kind of compression use the menu field "Compression". A click on the menu field shows a pop up menu with all existing types of packers. Some packers need individual settings to tune the compression (pack ratio, speed, memory usage, etc.). A settings window is provided for this kind of packer. A click on "Settings" opens the window for the selected packer. If a packer needs no settings, the settings button is disabled.