I have a very large folder of MP3 files which always errors out on backup my my Linkstation to an attached USB drive. The error in my backup file said
'rsync error: received SIGINT, SIGTERM, or SIGHUP (code 20) at rsync.c(541) [sender=3.0.3]'
this is an indexing error. Create a new folder, copy the contents to the new folder and this should fix the indexing error.
Have you formatted the usb drive to xfs through the buffalo?