[seized]

No, only for deduplication, which is optional and doesn't make sense for most workloads. And usage depends on record (like block) size and other factors. Usually 1GB per TB of deduplicated storage is the max. ZFS works on datasets for configs like this, so you can dedup a small "filesystem" of data but not all 40TB on a pool.

It will use lots of RAM for ARC (adaptive read cache) but that can be limited.

ZFS RAM usage is greatly overblown in my opinion and experience.

[anotherhue]

Agreed. People forget how much more RAM we have now versus when ZFS was developed. It's like old emacs swapping jokes.