Database and file management help please!

Juggling Rekordbox databases is possible, tho you need to know exactly what you are doing.

A possible solution for your situation is creating 2 Rekordbox collections. One for the tracks on the external, and another one for the tracks on your internal drive.

both have the database in the default location:

~/Library/Pioneer/

this is the user level Library folder, not the one at the root of your drive.

Now here comes the trick

• create a Rekordbox collection with tracks from your external drive.
• quit Rekordbox
• rename the folder 
  ~/Library/Pioneer/
  into
  ~/Library/Pioneer External/
• start up Rekordbox (it will create an empty collection)
• fill this with the tracks from your internal drive
• quit Rekordbox
• rename the folder 
  ~/Library/Pioneer/
  into
  ~/Library/Pioneer Internal/

Now if you want to use the external collection

• quit Rekordbox
• rename the folder 
  ~/Library/Pioneer External/
  back to 
  ~/Library/Pioneer/

ditto if you want to use tracks from  the internal drive, but first make sure you rename the current /Pioneer/ folder.

You could even create a simple Apple Script that will quit RB, activate the desired collection and start RB.

This has "user error" written all over it, and those 2 collections are 100% separated, meaning DJ metadata you change in one collection would not show up in the other (think about cues/grid/loops/playcount/starratings etc)

A different approach using the same method is creating a CDJ USB with the tracks you want from the external drive, switch database and then import the contents of that CDJ USB in the (empty) Rekordbox collection.

This is more work, the import function of Rekordbox has a known bug where cues/loops are not always imported the first run (requires a 2nd import of the same usb). But the tracks of the USB will be copied to the internal drive (it's an import option) so creating your "internal" collection.

This method maintains all DJ metadata from the "external collection".

And you can always look how I manage my workflow. All my tracks are on a AppleShareFileserver (=external drive)

My Workflow Summer 2020, using the new iTunes Collection Tool. Live recording unedited

Another related tutorial:

Why cues, loops etc can disappear from your DJ software aka filepaths matter

Option 1: Throw everything in one database (internal), keep all music external, effectively use MyTags and playlists to manage music.

Option 2: Try and juggle two databases and pull out hair when things go sideways.

Thanks for the comments. MixMasterG your workflow video was interesting up until the point it involved iTunes. Not going there again. Part of the problems I have were cause by iTunes to begin with. Plus I use the iTunes xml to run Beatport Pro which I use for my custom tagging / comments. 

@Pulse, what would you anticipate to go wrong with two databases?

Part of my point was I don't want to have to keep my external drive plugged in all the time to launch and work with Rekordbox.

If I do it your way, then I'm either dependent on the external drive for my tracks, OR I keep a limited number of tracks on the internal drive and have a bunch of broken links for the rest pointing to the external. 

I *think* I might be happy with my solution above. I got it running, and so far it seems good for me. I have a smaller db, collection & set of playlists on the internal HD that I can work with, then a larger database and full collection at my fingertips when the drive is plugged in.

r. 

Don't get me wrong, I'm not trying to force "my method on you" but here is some background info you may need:

iTunes doesn't have to be a deal breaker if you know what you're doing, see this video (I explain it in the workflow video as well because it's iTunes/RB problem #1)

Why cues, loops etc can disappear from your DJ software aka filepaths matter

regarding the XML's from Beatport/iTunes, this might be of interest (and if you are on Catalina on RB6, then RB can bypass the itunes.XML and use the API)

Tutorial: XMLfiles explained for DJs in under 6 minutes

From a support perspective @Pulse's discouragement for using 2 main databases is understandable. Like I said, the method has user error written all over it. But if you follow my live streams then you see me do it all the time (for umm the past 5 years) and never caused any issues.

And 2 databases is the only way to accomplish what you want, a main "external tracks database" and an "internal tracks database" which is a subset of the external.