Ask HN: Database for efficiently storing many numpy arrays

I'm looking for a database that can store dense N-dimensional numpy arrays. Query performance is not as important as storage efficiency, the arrays are dense but mostly 0's and 1's and compress well.

I tried pg's array support (very slow) and storing it in pg's JSON field (also quite slow, but more acceptable)

I should also add, we're going to be writing a lot more than reading -- potentially for many processes, so anything with ACID-like support would be great.

But there must be dedicated databases out there for dense numerical data like this?