I used a rockpro64[0] with an off the shelf PCIe SATA card for my home NAS (4x4TB disks). So far I'm extremely happy with it (using it for almost 8 months). The rockpro is running debian/ZFS.
Interesting! I've been thinking of building a NAS and hadn't considered the rockpro64. Have you found that 4GB RAM has been sufficient for ZFS? I'm currently running a small ZFS array with 12GB RAM and the box never seems to use anything close to that amount, but ZFS has a reputation as something of a RAM hog.
I'm not using de-duplication, so that might affect if you only have 4GB RAM. Right now the box has 2GB free, and I'm always running a few extra things in it. Overall, for my use case it works just fine. The SATA card is plenty fast as well. I had a similar setup with an rpi3 and a USB<>SATA to host 2x1TB disks and doing a scrub in that pool took over 4 hours. The scrub in my current pool (4x4TB) took 22 min.
