@girish Your question got me wondering what was going on.
Turns out, two apps on the volume both had caches that were insane (one due to an old uninstalled WP cache plugin that was removed, but maintained its 12 MILLION cached files, and the other was Mastodon, which needed some manual cleaning for the 800k files it had cached).
Turns out there were just SO MANY folders/files that any attempt to backup or read the size would just time out.
D'oh!