I use mergerfs too. I ended up with all the drives under mergerfs running on bcache with a single SSD as the cache. Mergerfs's documentations brings up ways to

I use mergerfs too. I ended up with all the drives under mergerfs running on bcache with a single SSD as the cache. Mergerfs's documentations brings up ways to do tiered caching: https://trapexit.github.io/mergerfs/preview/usage_patterns/ https://trapexit.github.io/mergerfs/preview/usage_patterns/ . Though it doesn't really do a read cache. It only keeps the newest files on the SSDs. I hope bcachefs (not bcache) gets better. It supports combining multiple different slow drives like I do under mergerfs, and also a file level cache on SSDs. And even supports keeping metadata on the SSDs completely. Erasure coding isn't done yet either, so that's no replacement for SnapRAID.