Okay going to restart Mastodon processes... let's see just how much hell breaks loose.
Haha ok all media is broken haha. Let's now try to move over media. (Nothing's been deleted, the configuration is just referring to a different location 
)
Actually, let's see what happens if I upload a new piece of media... Oh okay, a 500 error, that's not good probably.
Okay I got the b2 cli working on the server and the account is properly authenticated, so I know the id and secret key are correct... so I can't figure out why I'm getting the 500 error, hmm.
On the theory that the upload 500 error is because the media directories aren't synced with the bucket, I'm doing a dry run of the sync and wow... the sheer number of cached avatars & headers from remote servers is... concerning? It was nothing but avatar caches for a few minutes now, and it's moved on to headers just now. The lack of any user-level mechanism for cleaning these files up has been pointed out as a problem, I believe.
Okay I think I'll run a cleanup of inactive/deleted remote accounts first, that's quite a few media files there and I don't want to transmit unnecessary files.
Doing a dry run of tootctl accounts cull and it's just passed 1,000 of 74,818. Probably a good time to step away.
Dry run shows 932 accounts being culled, so... I guess it's worth it? Not entirely sure if it'll get rid of the cached avatars, but I'd been meaning to run this cleanup job anyway.
Accounts culled, though it doesn't seem to have done a huge amount disk space-wise. Running media file synchronization now.
All right, the instance is running and media uploads seem to be working again, though there are sporadic failures that I'll be watching & tweaking for while we try this for a few days. Hang on, folks!
Wow cache is far and away the biggest directory of media files so far, and accounts/avatars alone takes up 4.9 GB. And that's with a blocklist a mile long including the biggest instances at mastodon.social and .online. No wonder media cache cleanup did so little, since it evidently doesn't do anything about cached remote avatars. Very glad to be getting all this off the server's limited disk space--now if only I could get the server to serve these images! :P