sparse files are efficient but they break NFS quota accounting. we run ~10k pods and found that usage reporting drifts and rehydration latency causes weird timeouts. strict ext4 project quotas ended up being more reliable for us.

I’ve used this technique in the past, and the problem is that the way some file systems perform the file‑offset‑to‑disk‑location mapping is not scalable. It might always be fine with 512 MB files, but I worked with large files and millions of extents, and it ran into issues, including out‑of‑memory errors on Linux with XFS.

The XFS issue has since been fixed (though you often have no control over which Linux version your program runs on), but in general I’d say it’s better to do such mapping in user space. In this case, there is a RocksDB present anyway, so this would come at no performance cost.

I am guessing the choice here is do you want the kernel to handle this and is that more performant than just managing a bunch of regular empty files and a home grown file allocation table.

Or even just bunch of little files representing segments of larger files.

We can talk about even more general idea of saving file space: compression. Ever heard about it used across the whole filesystems?