Solved! Go to Solution.
Before tuning: 19MB/sec (default values)
Second tuning attempt: 49MB/sec (using 128K block size, 64 buffers)
Final result: 129MB/sec (using 128K block size and 256 buffers)
Since it's a LOT3 drive have a native transfer rate of 80MB/sec any further tuning attempt are meaningless.
If your backup is still going slow you should tell us more about the configuration (OS, hardware, file system, number of files, tape drives, etc)
Maybe it's the file system it self. It can be tested with the
# time /usr/openv/netbackup/bin/bpbkar -nocont -nofileinfo -nokeepalives / > /dev/null 2> /tmp/file.ou