Most NAS on the market are built around an ARM SBC with similar or better compute specs to the RPi and run Linux (often Debian). Honestly I think the Synology N

Most NAS on the market are built around an ARM SBC with similar or better compute specs to the RPi and run Linux (often Debian). Honestly I think the Synology NAS even has a bigger and more helpful community for running these kinds of applications than the RPi does. There are also some more tinkerer-oriented NAS products such as the Kobol Helios machines that even offer GPIO - but also USB-C direct-attached storage and 2x gigabit (or better) ethernet interfaces, in the most recent model. When you consider the additional pain point of dealing with USB SATA controllers, I'm not convinced the RPi would ever be a good choice for a NAS or home server unless you were choosing it strictly for price reasons - NAS features like a good enclosure and drive management are unfortunately very steeply priced compared to the RPi, with commercial products often running $600 and up... although the Kobol products are very attractively priced, at the cost of very long fulfillment times since they run on preorders.