DLT tape gives only half blocks back of what was written.
Some 11 Tb was dumped for me on 330 DLT tapes using a blocksize of 512Kb.
When I read those tapes on a HP target machine I get only the 1st half of every block.
Funny that it doesn't matter if I use dd with bs=256k or bs=512k, the result is the same:
the first 256Kb of every block. Even a JAVA 1.4 program using RandomAccessFile to byte[512*1024]
produces the same result.
I presume that the original writing program (in C) wrote some SCSI commands to the drive
in order to get it to write (and read) 512 Kb blocks.
Who knows how to archieve the reading of all 35Gb per tape?