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.
If you want that long tail, bandcamp and soundcloud are better sources. The barrier to entry is low with those, and there’s a plethora of small, niche artists just doing their own thing.
For a representative snapshot of music though, it’s pretty amazing. It shows what a massive percentage of the planet listens to, preserved hopefully across many seeds, and historians will love shit like this in the future.