FreeNAS != ZFS. The former is a specialised storage system that has to meet a very different set of criteria than a lightweight server with 1GB ram.
My main issue is to be able to repair a "silent" data corruption on a single drive machine. Am I able to use x% of my "partition" to data repair or do I need to use other partition/drive to mirror/raid it?
If I understand right zfs can detect bitrot ("not really" a big deal) but without any local copy It can't self heal.
My use case is an arm A20 SoC (lime2) to storage local backups among other things, so I need something that detects and repairs silent data corruption at rest by itself (using a single drive).
A poor man NAS/server. ;)
Ideally, though, please add an additional disk and set it up as a mirror.
ZFS can detect the silent data corruption during data access or during a zpool scrub (which can be run on a live production server). If there happen to be multiple copies, then ZFS can use one of the working copies to repair the corrupted copy.
Anyway I will try to use it for my main PC which has several disks and continue to use my solution for single disk machines (laptop, vps, SoC...). :)
In order to achive the same with ZFS you have to run RAID-Z2 on sparse files.