I would like to know how much ram do you really need in order to run zfs? I have always stayed away from ZFS because from what I've read it seems to be a ram hog.
If you are satisfied with pure disk performance, 1-2 GB RAM is ok for a ZFS Server.
But pure disk performance is bad especially with multiple user and small files.
This is where ZFS needs RAM to cache all reads.
It is quite normal on a good ZFS server that most (>80%) reads are delivered from RAM Cache 100 times faster than from disk. This is why ZFS uses nearly all RAM dynamically on heavy use and even 128GB+ of RAM can make sense.
Some people think this is bad, but this is perfect.
You use all RAM that you have bought to increase performance not for silly high idle values.
With Solaris, this is done automatically, with BSD you mostly need some tweaking.
But be warned.
This is only true without dedup. You should never use it unless you know about the RAM needs and have good reasons to do.
In general, disable dedup and enable compress (best compress is LZ4 on Illumos based systems)