> I'm testing our new changer which is equipped with 2 LTO-4 drives. > What should I expect from LTO's hw compression? On LTO2 and DLT I have seen between 1.1:1 to 2.5:1 but mostly between 1.4:1 and 2:1.
> I've seen LTO-3 tapes with > 800+ GB data. Here are the volbytes number I got with LTO-4 so far. > > volbytes: > 1,164,080,268,288 > 1,138,440,038,400 > 1,180,908,417,024 > > This is a compression ratio of 1,45:1. > > I know that these numbers are highly dependent on the kind of data > that is backed up. > > The data I'm currently backing up is mainly made up of large hdf > files. > > # du -sh * > 1,4G 16bit_chan0.hdf > 0 16bit_chan0.hdf_pdetTrigger.log > 325M 8bit_chan0.hdf > 201M 8bit_chan1.hdf > > # bzip2 * > > # du -sh * > 447M 16bit_chan0.hdf.bz2 > 4,0K 16bit_chan0.hdf_pdetTrigger.log.bz2 > 219M 8bit_chan0.hdf.bz2 > 652K 8bit_chan1.hdf.bz2 > > > So bzip2 seems to be able to compress the data far better (3,4:1), but > the drive has to do it in "real time", thus is might be slower, > although compression is implemented in hardware. > It has to do this at 120 MB/s for LTO4 drives which is a lot faster than any software compression I have seen. I would consider the compression closer to gzip fast (or LZO) than bzip2 and also there is one big difference the hardware compression in the tape drive compresses block size chunks at a time instead of the whole file. > > I'm just wondering if I have to set a special density code with mt > (which I don't know at the moment)? Doubtful. I have never seen a tape drive with variable compression methods. John ------------------------------------------------------------------------- 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
