Indeed you were right as the volume was created on a DS213air before I moved it to a HP Proliant N54L, without knowing that DS213air specs limits the volume size to 16TB, and DSM isn't able to go beyond after a NAS migration.
Now my big problem is that deleting the volume also forces me to delete the packages, and from what I could find on internet, there is no way to make a backup of them with my custom settings, or the playlist database of Audio Station...