Testing LTO drive with mt and dd

Here are my commands mt -f /dev/st0 rewind dd if=/dev/st0 of=- As I understand it the first command rewinds my tape in /dev/st0, and the second command writes contents of /dev/st0 to -. My questions are - Where is -? - What is this command doing when it writes the data from the tape to -? The result of the command is: dd: writing to '-': No space left on device 1234567+0 records in 1234566+0 records out 140000000000 bytes (141 GB) copied, 14500.9 s, 9.8 MB/s It appears to me I have written the data to something, but I would like to verify where that data was written. Is it just reading the tape? Thanks for the help