> > can anyone advise me how to determine the block size of this tape?
>
> mt -f /dev/... status
>
> reports the blocksize that the device is configured (not that tape
> that is in it).
>
> If you read a tape, specify a blocksize larger than then one on
> tape (maybe it has to be an exact multiple of it, never tried all
> possible combinations. e.g. try:
>
>    dd if=/dev/... bs=256k
>
> Some implementation of dd need "ibs=..." instead of "bs=..." to
> force a blocksize when reading (and obs=... to force for writing).
>
> It's best to specify variable blocksize (by specifying 0 for the
> command).  It's the most flexible, for those drives that support it
> (any modern drive, I believe).

seems the issue was a dodgy SCSI cable from the box to the drive. Swapped it
out and it all works fine.

thanks all.

Tom