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Compression bug?


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I've found the following oddity with Retrospect 6.0 (using Sony DRU-120A DVD+RW):




Full backup with compression:


First DVD takes 776 files (3.1Gb), total of 5 DVD+RWs required, last DVD+RW used 2.9Gb




Full backup without compression:


First DVD takes 1095 files (4.4Gb), total of 5 DVD+RWs required, last DVD+RW used 0.8Gb








The bulk of my files on the first 2 DVDs are my music collection - OpenMG format. Looks like turning on compression actually expands them!




I had the same issue with Retrospect 5.6, so I upgraded - only to find the same problem.




What is going on? If the compression algorithm hits a data file with nigh-on random (=> uncompressable) content, does it expand in size?!?




Help! :-(







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Actually this is not a bug. Compressing a file that is "pre-compressed" will often result in the file growing in size. You can see the same thing with .zip or .sit archives.




Retrospect has a built in filter that tells it not to compress specific pre-compressed files. That filter probably does not currently contain your specific file types.




If you want to try an advanced (and unsupported trick), try this:




1) Launch Retrospect


2) Click on Configure


3) Hold down the Shift Key on the keyboard


4) While holding down "shift" click on Selectors


5) Edit the "Compression Filter" to include your audio file types.




We also have a compression FAQ available:





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