> > We've been using LTO3 tapes with bacula for a few years now. Recently I've > > noticed how variable our tape capacity it, ranging from 200-800 Gb. > > Is that strictly governed by the compressibility of the actual data being > > backed up?
Hello, the lower bound 200 GB on 400 GB LTO-3 tapes is not possible due to the drive compression, because it always compares, if compressed data are shorter that original. In other case, it writes data uncompressed. So, in all cases, you should see atleast 400 000 000 000 bytes written on all tapes. > > Or is there some chance that bacula isn't squeezing as much > > onto my tapes as I would expect? 200Gb is not very much! In bacula, look mainly for the reasons, why there is just 200 GB written. If the tape is full, think about these: - Weared tapes. Typical tape service life is written as 200 full cycles. However, read http://www.xma4govt.co.uk/Libraries/Manufacturer/ultriumwhitepaper_EEE.sflb where they experienced problems with some tapes just only after 30 cycles! How many cycles could you have with your tapes? - Do you use disk staging, so that tape writes are done at full speed? Do you have a good disk staging? Considering using SSDs for staging is very wise. If data rate is lower that 1/3 to 1/2 of native tape speed (based on drive vendor, HP or IBM), then drive has to perform tape repositions, which means another important excessive drive and tape wearing. My experiences are, that even HW RAID-0 with four 10k disks could not be sufficient and when there are data writes and reads in parallel, it could not put 80 MB/s to the drive, typically just 50-70 MB/s, which is still acceptable for LTO-3, but not good. Currently, I have 4 x 450 GB SSDs HW RAID-0 with over 1500 GB/s without problem running writes and reads in parallel and just after that I hope that it is really sufficient for >= LTO-3 staging and putting drives and tapes wearing to minimum. - Dirty heads. You can enforce cleaning cycle, but then return to the two points above and other suggestiong, like using some monitoring like ltt on Linux (or I have some home made reporting tool using camcontrol on FreeBSD), where it would be possible to ensure, that your problem are weared tapes, or something else. Best regards. -- Rudolf Cejka <cejkar at fit.vutbr.cz> http://www.fit.vutbr.cz/~cejkar Brno University of Technology, Faculty of Information Technology Bozetechova 2, 612 66 Brno, Czech Republic ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users
