Hi, Thanks for your explanation. I checked with the status with the mt command.
# mt -f /dev/nst0 datcompression Compression on. Compression capable. Decompression capable. This looks to me, as the compression would be enabled. I had the same issue on my old debian box. It was always just writing around 33GB on the tape, never more.The data I try to backup are alot of Word-Documents and all different kind of sourcecode. So there should be at least some compression. I might try the software compression from bacula and see if that helps. But if you have some idea what else I could test I would be very glad. Thanks, Oliver > Hi. > > [EMAIL PROTECTED] wrote: > >> Hi all, >> >> I have a HP DAT72 tape and installed it on a new debian sarge box. The >> problem I have is the following: >> I defined the tape with hardware compression: >> - I used the following command: mt -f /dev/nst0 datcompression 1 - I >> did not enable software compression with bacula. >> >> When I backuped several directories which are holding around 50GB the >> backup stopped after 33,900,640,561 bytes. This is not even the Amount >> the tape should save with compression disabled. >> What do I have to do to enable hardware compression? > > First thing is to check that compression is actually enabled: mt status > or tapeinfo might tell you. > > Second thing is a completely different question: How to determine the > usable tape capacity? > > Some (sort of) facts: Manufacturers give highly optimistic values: Your > example: DAT72 means "raw" capacity of 36 GBytes. In "manufacturer > mode" this is 36000000000 Bytes, of which you lose the space occupied > by End-Of-Anything marks. > Compression ratios are usually assumed to be 1:2, 1:2.6 (Sony) or even > higer (I forgot...), but in fact real-world data compresses quite > different. From my backups: I get between 18GB (with 1 GB = 2^30) and > 29 GB on a "20/40GB" DLT tape, with an average of about 22GB. Daily > incremental backups get great results for marketing purposes: up to 12 > GB on a DDS-2 tape (4/8 GB) - mostly log files which compress great. > When I store compressed digital media like mp3 of digital video files I > have about 3.5 GB on the same sort of tape. > > Conclusion: If you want to know how many bytes fit onto a tape you need > to measure the right thing: > For example, use 'dd if=/dev/urandom bs=32k of=/dev/st0'. Try with > varying block sizes and try with a number of 'mt weof's in between. Try > storing _your_ real data using tar, also trying different block sizes > and number of files. Then try the same with data compression. > > After some days you can draw some fine charts which tell you two > important things: How many tapes you need, and that the capacity > numbers given by the manufacturers have not much in common with what > you > encounter on a day-to-day basis. Forget the rest... > > I usually wonder when I see a tape marked "Full" with less then half > the nominal capacity (often indicates a broken tape) or "Append" at > three times the regular capacity (most often by chance the right sort > of data). > >> Thanks for your help, > > I don't know if that helps, but it might explain things. > > Arno > >> Oliver >> >> >> >> >> ------------------------------------------------------- >> SF email is sponsored by - The IT Product Guide >> Read honest & candid reviews on hundreds of IT Products from real >> users. Discover which products truly live up to the hype. Start >> reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click >> _______________________________________________ >> Bacula-users mailing list >> Bacula-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/bacula-users >> > > -- > IT-Service Lehmann [EMAIL PROTECTED] > Arno Lehmann http://www.its-lehmann.de ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users
