[radiowave]

I've run ZFS on OpenSolaris, Illumos, and then Linux, continuously since 2009. (However, I have no experience of using it on FreeBSD.) I've always regarded FreeNAS's RAM recommendations as being weirdly high. The "1GB per terabyte" thing dates from when ZFS systems were being pushed as enterprise workgroup file servers (i.e. maybe hundreds of users), with all storage on spinning rust. I wager that a great many FreeNAS systems are seeing approximately one user, primarily accessing large media files which mostly don't benefit that much from caching. Though of course, if you really are using FreeNAS in a more demanding role, then the hardware should reflect that.

I believe it did used to be the case that the FreeBSD port of ZFS had an issue where ZFS wouldn't always back off its RAM use fast enough, if the system came under memory presure, so it was at the time prudent to ensure that FreeBSD ZFS machines never got into low-memory situations, but I haven't heard anybody complain about that in practice in some years, so presumably it's fixed now, but FreeNAS's RAM recommendations have not been relaxed.