I believe usb disks are poor targets for rsync because the program runs many instances of itself, if you want it to continue being responsive [ but the backup will take much longer ] use the --bwlimit= parameter. For USB I would use 900 and see if the lockups are fixed, and bump it up if so until you find its practical limit there. 9000 is almost full speed. [ Not certain to be a fix, but worth trying ]I would really like to avoid using a workaround for rsync. It's really a big part of my backup strategy. Unfortunately, thunar is not providing any info on what it was doing, but I think it being stuck was related to the rsync process running in the background.