If a modern "one-shot" tape drive encounters an error during write, it will write the data again as the tape is moving. You lose a little bit of total capacity

If a modern "one-shot" tape drive encounters an error during write, it will write the data again as the tape is moving. You lose a little bit of total capacity, but the data will still get written. This is why you always plan to write a little less than the full capacity of your tape. Newer LTOs may behave a little differently, I haven't kept up with newer stuff here.