NanoPi M4 can now be used as a multi-drive NAS with new HAT expansion board
The NanoPi M4 is a powerful single board Linux computer, and with the addition of this new addon HAT it can directly power four SATA drives. With a suitable case you can easily build a RAID NAS using OpenMediaVault for a very cheap price. This combination should offer similar capabilities to the Drobo 5N I have - both run Linux on an ARM CPU and support several SATA drives. The difference being that with the NanoPi M4 one has an open system to configure as desired, whereas with the Drobo is closed and hard to customize.
NanoPi board and accessories buying guide.
DIY makers around the world are building customized computerized gizmos thanks to the Raspberry Pi, and similar computers. These diminuitive computers pack a lot of computing power, at low energy requirements, and by running Linux they are more approachable than microcontrollers like the Arduino. The Raspberry Pi is the best known of this class of computer. Because of the very large user community, there is a ton of accessories, books, tutorials, and more focusing on the Raspberry Pi.
NanoPi-M3: 8 blazing cores, but... // Review
The NanoPi-M3 has 8 1.4GHz ARM cores, 1 GB data, 1+ GHz CPU, 1GHZ Ethernet, and a number of useful ports. The CPU generates a lot of heat so a heat-sink is necessary, except it's danged difficult to mount one. It has more GPIO pins than the Raspberry Pi. There's a number of ports on various chips that aren't exposed to users. It has enough warts that one might not want to use this, unless high parallel computation rate is needed thanks to the 8 cores.