Well I have inherited this pile of DLT-4000 tapes which were written with the command .....

tar cvf - somefiles | dd of=/dev/nst0 bs=256k

Now it falls to me to restore this data .... but (and yes I rewound the tape )

dd if=/dev/nst0 bs=256k | tar xvf -

fails ..... some files can be read fine but mostly it starts reading the file and then says skipping to next file header, and the file read back from tape is truncated

Maybe I am ignorant but it seems to me this is becase the block size coming out of tar is 20 x 512 bytes while bs=256k sets both the input and output size to 256k.

So I tried a scratch tape with ...

tar cvf - somefiles | dd of=/dev/nst0 ibs=10240 obs=256k

and recovered with

dd if=/dev/nst0 ibs=256k obs=10240 | tar xvf -

which works perfectly

So ..... how can I get the data back from these tapes properly???

Thanks in advance for any help you can offer (otherwise I will be expected to fall on my sword at work .....)

S.