I’m using Volumio 2 with a usb disk connected to the RasPi 3.
I put some musics on it and I played them.
After a while I have reformatted the disk and I put on it other music.
After have restated the system I did the re-indexing in My Music.
But from the web interface I can see the old music and play them. It’s mixed to the new one.
With a file manager on another Linux however I can’t see the old files it on the disk.
Instead with web browsing and choosing USB I find also the old directories and the related files.
Where are they hiding? 
How can delete them completely from the system ?
I would have expected that Volumio “forgets” the original tracks when you update or rescan the library. Possibly you need to reboot as well.
If you can play them then they must still exist (somewhere)… Are they in your INTERNAL folder? (/var/lib/mpd/music). So far as I know you can’t play a file that doesn’t exist! If you find away to do that then please let me know
I agree. That’s what my 40 years spent on computers suggest also to me … 
No, the files are not in INTERNAL, but on /var/ lib/mpd/music/USB placed on SD card.
I did not create this directory, but I copied the files on it via SMB, thinking it was the external disk connected to Volumio because I was seeing on it the external disk directories.
There is also another with name NAS.
If It’s enough clear to me what the directory INTERNAL is, less clear is what USB and NAS directories are and why both are on SD card.
So I reformulate the questions: what are the service of the USB and NAS directories?
Can I transfer via SMB to the disk connected via USB? Or should I unplug the disk from Volumio, connect it to the source system and copy the files on it?
That is, via SMB can I transfer files only on SD card ?
Thanks.
My guess would be they are directories used for the mount points, analog to the option folders in browse. Used for mounting the actual NAS/USB directories to
Sent from my iPhone using Tapatalk
As kaosmagix says. The directories you refer to (in /var/lib/mpd/music) are symbolic links for the benefit of mpd pointing at mount points in /mnt.