On Fri, 30 Dec 2005, Ken Schneider wrote:
On Fri, 2005-12-30 at 13:18 +0000, KRAMO FIACRE wrote:
Hi!!! I've got an HP SURESTORE DAT 40 on my SUSE LINUX ENTERPRISE SERVER 8 BOX SP3. The tapes I use are marked 20/40GBYTE. But I can only make backup up to 20G, whereas on my ALPHA server with tru64 unix, I can save up to near 40 Gbytes using the dev file "/dev/rmt0h" (for tru64 V 4F) or "/dev/tape/tape0_d1" (for tru64 V 5.1B). I try to enable compression using the command "mt -f /dev/st0 datcompression 10", this command achieved succefully but nothing. I try to use the /dev/st0m or /dev/st0a, but these devices files seem not to be associated to physical device. So how can I perform backup with hardware compression? Please help
You may need to turn on compression after every reset of the tape drive.
Indeed. Try using mt -f /dev/st0 datcompression 1 <<- not '10'
Also remember that you will never get 40G of data on the 20G tape using compression. Binary files never compress 50% and actually compress very
Neither of those statements are strictly true. I've seen ratios of 10:1 or better. It all depends on the nature of the data that you are backing up. Now, I don't know if hardware compression can do quite that well, but gzip certainly can, and bzip is even better (although *far* more expensive).
little and some even get larger when being compressed.
Also I don't recommend using software compression and hardware compression together.
That's good advice. -- Carpe diem - Seize the day. Carp in denim - There's a fish in my pants! Jon Nelson <jnelson-suse@jamponi.net>