PiNAS: Make your Raspberry Pi into an affordable NAS
Off the bat, we should point out that the PiNAS is not an off the shelf unit. Instead, you must feel comfortable soldering, using a glue gun and have access to a 3D printer or a 3D printing service.
If you are still with us, then the PiNAS comes from AraymBox, a member of Instructables. In short, PiNAS allows you to turn a Raspberry Pi into a NAS with two drive bays. According to AraymBox, the PiNAS supports the Raspberry Pi 2 and Raspberry 3. The project supports the Raspberry Pi 4 too, but some minor adjustments are needed to get the SBC working with the PiNAS.
According to the guide, you will need a microSD card, a micro USB breakout port and two SATA to USB adapters to create the PiNAS. A power supply, numerous screws and nuts, a Raspberry Pi and two 2.5-inch drives are needed too. You can download the full instruction set and parts list from here.
The PiNAS can support Wi-Fi too if you would rather not use a wired connection. The build looks easy to maintain or upgrade. Incidentally, the PiNAS leaves two of the Raspberry Pi's four USB Type-A ports free, allowing you to connect external peripherals.