Andrea Conti wrote: >> 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. > > I think it was HP DDS media (or perhaps drive docs) that explained that non-technical data was more compressible than technical data. I guess the animated children's shows that I'm backing up are much more technical than I had imagined :-).
> Also note that DAT is old stuff: I don't really know how much better > hardware compression modern tape drives provide. > > DAT compression really is pretty bad--when I was using DDS4, I would routinely get only 17G on a tape that could natively hold 20G. In those cases, the files were MPEGs, so I wasn't expecting much, if any compression, but I wasn't expecting a 15% expansion. I resorted to turning off h/w compression on my DAT drive, since my biggest backups were mostly non-compressible. LTO2 has been much nicer to me--my smaller backups compress very well with LTO2 h/w compression, and I've yet to have any tape that was full with less that 205G of data on it (LTO2 is 200G native). My assumption is that LTO compression detects when expansion will happen and stores the data uncompressed when necessary. In my case, my average full LTO2 tape holds about 250G, with my 'best' one holding 310G--but my backups are probably much more 'technical' (see above) than is typical. > Andrea > > > -se ------------------------------------------------------------------------- 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
