OK, here is my solution that allows full tape length for my backups. Notice that I am using amtapetype only as an effective way to illustrate both my problem and the solution.
This demonstrates using the OS and mt to turn tape drive hardware compression ON: * Michael D Schleif <[EMAIL PROTECTED]> [2005:06:17:10:04:59-0500] scribed: <snip /> > # sudo /bin/mt -f /dev/nst0 compression 1 > > # sudo /bin/mt -f /dev/nst0 defcompression 1 > > # sudo -u backup amtapetype -c -f /dev/nst0 -o > Writing 1024 Mbyte compresseable data: 384 sec > Writing 1024 Mbyte uncompresseable data: 1318 sec > WARNING: Tape drive has hardware compression enabled > Estimated time to write 2 * 1024 Mbyte: 2636 sec = 0 h 43 min This demonstrates using the OS and mt to turn tape drive hardware compression OFF: # sudo /bin/mt -f /dev/nst0 compression 0 # sudo /bin/mt -f /dev/nst0 defcompression -1 * Michael D Schleif <[EMAIL PROTECTED]> [2005:06:16:23:59:28-0500] scribed: <snip /> > # time sudo -u backup amtapetype -e 12g -f /dev/nst0 -o > Writing 32 Mbyte compresseable data: 37 sec > Writing 32 Mbyte uncompresseable data: 35 sec > Estimated time to write 2 * 12288 Mbyte: 26880 sec = 7 h 28 min > wrote 298832 32Kb blocks in 76 files in 10632 seconds (short write) > wrote 310628 32Kb blocks in 158 files in 10840 seconds (short write) > define tapetype unknown-tapetype { > comment "just produced by tapetype prog (hardware compression off)" > length 9522 mbytes > filemark 0 kbytes > speed 908 kps > } > > real 364m39.451s > user 0m2.724s > sys 0m28.719s Next, the Compaq/Sony SDT-9000 a physical jumper labeled `disable dc'. To this point, this jumper was OPEN. Now I CLOSED this jumper. Interestingly, now when I used the OS and mt to set both compression and defcompression to 1, the following test _never_ returns an initial estimate: # sudo -u backup amtapetype -c -f /dev/nst0 -o Finally, with the jumper CLOSED, compression 0 and defcompression -1, I get the following: # time sudo -u backup amtapetype -e 12g -f /dev/nst0 -o Writing 128 Mbyte compresseable data: 114 sec Writing 128 Mbyte uncompresseable data: 114 sec Estimated time to write 2 * 12288 Mbyte: 21888 sec = 6 h 4 min wrote 365676 32Kb blocks in 93 files in 11010 seconds (short write) wrote 365676 32Kb blocks in 186 files in 10484 seconds (short write) define tapetype unknown-tapetype { comment "just produced by tapetype prog (hardware compression off)" length 11427 mbytes filemark 0 kbytes speed 1089 kps } real 373m59.100s user 0m2.907s sys 0m30.466s Most importantly, last night's backup used nearly the whole 12 GB of tape! Thank you, all of you, for your contributions to this challenge. -- Best Regards, mds mds resource 877.596.8237 - Dare to fix things before they break . . . - Our capacity for understanding is inversely proportional to how much we think we know. The more I know, the more I know I don't know . . . --
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