After T182450, this could be a generalized problems. Files to handle include:

• Old database files from databases that are no longer live
• One time local dumps/backups that are no longer necessary
• Rests of older binlogs
• Rests of xtrabackup log and other files

We need to identify them and delete them, as they could be taking a non-trivial amount of space. This is not a priority (there is no known ongoing isssues), and it has to be done very carefully, as it would be easy to delete by mistake used files and not notice after a restart, causing an outage. So this should have very low priority.