We backed up Spotify (metadata and music files). It’s distributed in bulk torrents (~300TB). It’s the world’s first “preservation archive” for music which is fully open (meaning it can easily be mirrored by anyone with enough disk space), with 86 million music files, representing around 99.6% of listens.
The politics of preservation is definitely an interesting one. I suppose one argument in favor of preserving more popular music is that there are going to be fewer popular tracks than unpopular tracks - and they’re already at 300TB, which is nothing to sneeze at, especially since it’s a third the size of their existing library of ebooks.