ASRock Rack C3558D4I-4L Atom C3558 Mini ITX Motherboard w/Quad GbE LAN, IPMI, 13 x SATA Connectors

This is a great option for a NAS server. However, be aware that "13 sata ports" is misleading. In the BIOS, you have the choice of using the PCIe card at 8x, 4x, and various combinations of SATA / SAS ports. Essentially you can pick 8x PCIe and 1 SATA port, 4x PCIe and 5 SATA ports, or PCIe slot disabled and 9 ports. If you were planning on hooking up 13 drives and throwing in another SAS controller besides, or even running an 8-drive data array plus a RAID1 system drive array, it's not going to work.

Performance wise, this board is what I expected. What isn't clear from the description or documentation is that due to limitations of the single-die Atom SoC (4 core) is that there isn't enough available bandwidth to feed the PCIe slot, SAS connectors and the 5 SATA ports at once. You have to choose a "mode" for the board, which selectively disables some I/O in favor of others.TL;DR version: you can only run a maximum of 9 SATA devices on this board at once, and you have to give up the PCIe slot to do it.