HP DAT 36/72 capacity (SCSI external)

[Dusan Jiricny]

Hello,
I'm not able to reach at least the native 36GB capacity under Linux. I was not succesfully backup even 35GB of data (using 'tar cvf /dev/nst0').

I made some tests.
[root@localhost ~]# dd if=/dev/urandom of=/dev/tape bs=1024 count=37748736
dd: writing `/dev/tape': No space left on device
27186100+0 records in
27186099+0 records out
This gives me 26GB capacity. Then I created the 36GB file with the same command above and stored it on the tape using 'tar cvf /dev/nst0'. Drive stored cca 35GB of data. I always rewound the tape before storing the data. I use drive blocksize=0 for /dev/nst0

I expected that I can store physically 36GB of data but I can't reach it. Could someone help me to determine what is wrong? (Most likely the 'thing' between the display and keyboard :-)