rsync couldn't delete what it copied

One of the drives in my MergerFS pool started showing pending sectors, so I mounted it read-only and rsynced everything off with --remove-source-files.

Two terabytes later, rsync finished the copy and then threw errors on every single delete. Obvious in hindsight: read-only was the whole point of the mount, and --remove-source-files needs write access to unlink the originals. The data was safely on the other side, it just couldn’t clean up after itself.

Remounted with mount -o remount,rw and ran the same command again. rsync skips anything already transferred, so the second pass was just the deletions and took minutes. Worth knowing before you panic at a screen full of errors.