You want 16GB for ZFS.

Yes. 16GB is the sweet spot for a home NAS running TrueNAS with ZFS. 8GB will work, but you’ll notice the difference in anything beyond basic file serving.

ZFS is greedy for RAM because it uses ARC (Adaptive Replacement Cache) to keep frequently accessed data in memory. More RAM = more caching = snappier transfers, especially if you have multiple users or run apps like Plex or Nextcloud. With 8GB, the ARC gets choked, and the system starts reaching for the disks more often. That kills performance.

Also, ZFS is notoriously bad at recovering from a low-memory situation. If you run out of RAM, things get weird. 16GB gives you breathing room. It’s not that much more expensive, and future-you will thank you.

Skip the 8GB unless your NAS is purely a backup target that nobody touches. Otherwise, 16GB is the floor.