[barrkel]

FWIW, I run 10 x 4TB raidz2 NAS with 4GB using ZFS on Linux.

ZFS on Linux isn't as memory-efficient as it would be on FreeBSD, which has a much closer file system cache / memory manager architecture to Solaris, but it works fine.

ZFS memory consumption really rockets when you want to use dedupe, which basically wants to store a hash of every block in memory. The sweet spot for its use is in things like multiple VM images - where there's a lot of duplication inside large files that are otherwise different. But there's often ways to structure things to gain back the same space, e.g. with stackable file systems.

Without dedupe, and for a NAS scenario where there isn't going to be a massive working set (typically source or sink for backups, streaming video, etc.), 4G has been more than sufficient for me for years.