Current LTO drives require to be fed at hundreds of megabytes per second for writing. This is well beyond what 1-gig Ethernet can do. Does you NAS support that?

(You can occasionally get away with slightly lower feed speed -- the drive will write "invisible empty data" to keep the motors running and tape movement going -- but that cuts into capacity of the media in unpredictable ways. And eventually the drive decides it is facing data starvation and stops writing. The result of that is a few seconds of tape repositioning to restart the writes.)