> That "400G with compression" is just an average. There's no guarantee > that you'll get 2x compression. Personally, I find it false advertising, > but nobody's listening to me.
2x compression is indeed unrealistic most of the time. On a different note, some time ago I found myself wondering how effective hardware compression is when compared to software compression in the backup program, so I did some testing to see how much data from the same fileset I could fit on the same tape with different settings. The tests were done with a DDS3 tape (12GB native capacity) in a Certance DAT72 drive. Sample fileset was about 25GB from a windows machine, including the system disk (lots of binaries) and a 20GB assortment of images (mainly compressed textures) and text files. Tested compression settings were: - hw compression, no sw compression - hw compression, gzip -9 sw compression - no hw compression, gzip -9 sw compression Gzip compression was applied on a file-by-file basis, not by piping a tar archive through gzip. Results: - hw only: 16158925621 bytes - hw + gzip9: 17553548966 bytes - gzip9 only: 20472911550 bytes Please note that these figures cannot be directly compared from a compression ratio standpoint since they do not refer to the same data (more bytes means more files were included), but they do certainly provide a rough indication of the relative efficiency of the three combinations. Also note that DAT is old stuff: I don't really know how much better hardware compression modern tape drives provide. Andrea ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users
