As an FYI here's what I got with my DAT7000 (Quantum) drives....
~# mtx load 28 1 ; sleep 160 ; mt -f /dev/nst1 datcompression 2 ; amtapetype -f /dev/nst1 -t DAT7000_Compressed -e 70G ; mt -f /dev/nst1 rewind ; mt -f /dev/nst1 datcompression 0 ; amtapetype -f /dev/nst1 -t DAT7000_UnCompressed -e 35G ; mt -f /dev/nst1 offline ; mtx unload 28 1
Compression on. Compression capable. Decompression capable. Writing 256 Mbyte compresseable data: 27 sec Writing 256 Mbyte uncompresseable data: 60 sec WARNING: Tape drive has hardware compression enabled Estimated time to write 2 * 71680 Mbyte: 33600 sec = 9 h 20 min wrote 940417 32Kb blocks in 41 files in 7065 seconds (short write) wrote 951844 32Kb blocks in 83 files in 7178 seconds (short write) define tapetype DAT7000_Compressed { comment "just produced by tapetype prog (hardware compression on)" length 29566 mbytes filemark 0 kbytes speed 4251 kps } Compression off. Compression capable. Decompression capable. Writing 128 Mbyte compresseable data: 28 sec Writing 128 Mbyte uncompresseable data: 28 sec Estimated time to write 2 * 35840 Mbyte: 15680 sec = 4 h 21 min wrote 1066524 32Kb blocks in 93 files in 7193 seconds (short write) wrote 1072258 32Kb blocks in 187 files in 7412 seconds (short write) define tapetype DAT7000_UnCompressed { comment "just produced by tapetype prog (hardware compression off)" length 33418 mbytes filemark 0 kbytes speed 4687 kps } Unloading Data Transfer Element into Storage Element 28...done