>>>>> On Sun, 12 Aug 2007 15:57:54 +0200, Carsten Ralle said: > > Hi Martin, > > >> 1. Even with brand new tapes, on two different tape drives, using > >> continuous cleaning cycles, the tapes that used to store between 11.5 > >> and 13 GB uncompressed data on a windows machine only take about 8 GB > >> using bacula (same drive, same tapes). > >> > >> Following the advice to switch off software compression when hardware > >> compression is enabled, we run tests with following results (always the > >> same fileset of 23 GB uncompressed data) > >> > >> hw-compress sw-compress spool size data/tape total # of tapes used > >> on on 14 GB 8.2 GB 1.7 > >> on off 23 GB 12.9 GB 1.8 > >> > >> so we use the installation with both sw and hw compression turned on, as > >> it gives us better performance and less tapes/backup. > >> > >> Why is it impossible to store more then 8 GB on a 12/24GB tape. Again: > >> we ran the tests on multiple different drives (HP15xx and Sony > >> DDS3-drives). > > > > The problem is that DDS hw compression is not very good. In particular, > > when > > you use sw compression as well, the data written to tape actually gets > > expanded by the hw compression so your 8.2 GB of input gets written as 12 GB > > on the tape! > > Have you tried with hw compression off and sw compression on? > Yes we've tried. On the Sony drives there's a tool that reports > compression as disabled, but there where no changes in tape capacity, > though. According to the manual the drive switches are set to control > compression via software and if we turn off compression on a windows > box, it's enabled after pluggin the unit back into the Linux box. > So far we haven't noticed any difference with compression reported ON or > OFF.
Have you tried setting defcompression? I.e. mt -f /dev/... defcompression 0 mt -f /dev/... compression 0 Also, I suggest that you erase the tape after doing this, i.e. mt -f /dev/... rewind mt -f /dev/... weof to prevent the drive from picking up the old compression state from the tape. __Martin ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users
