file/directory only library option

[nosferatu_cat]

That's not the problem.  The tag database becomes a serious performance problem when the number of files reaches a certain level. It's a known problem.  In order to support tags you have to have the overhead of indices, etc.  The Raspberry Pi is not good with databases beyond a certain size.   I have enough files to have passed the critical point.  I've used tag editors.  They work.  I only use them when I'm dealing with player software that gets title/artist information from tags and ignores the file names.  I like the file/directory approach.  It has all the features I care about.  I can find anything I want quickly and get all the information I care about from the file names.  If I want discographical information I can look it up elsewhere.  Bonus, the file/directory approach requires minimal processing power.  There's some caching but storage of information is in my case in a separate location.  My files are on an NAS.  

There are many tag editor solutions that will take your folder hierarchy and tag the files based on that.  Doing so would replicate your meta data from the folders to the tags so it was still in the folders for your use, but also in the tags for moOde to use.