The blocksize of the tape device.
Tape-Blocksize
This value specifies how many
bytes are written to tape or read from it with one system call.
Usually this value is at least 512 or a multiple of it.
It is not very important if the blocksize is set to 2048
or 1024. The main thing to keep in mind is that if there is a
minimum, it should be respected (e.g. 1024 on AIX), otherwise
media space is wasted.