After 9+ years of continuous running my D-Link DNS-323 NAS is not powering up although the two hard drives in it are fine. OpenMediaVault is good software to run on a Pi with full GUI management of the NAS system along with RAID redundancy (yes you can also just run the Pi with RAID and SAMBA functionality too).
I like the Pi approach as it is easy to swap anything out that fails in the future. So although I could go for a neater more compact Quad SATA kit for Raspberry Pi 4 with enclosure, I'm going to use components that I already have. Because the Pi may struggle to power the two external hard drives I'm going to use a spare powered USB hub, and all I'll be buying is two USB-to-SATA adaptor cables to plug in and power the hard drives to the USB hub.
It will look a bit like the attached photo but with two drives connecting via the USB hub. This way I can add another two drives quite easily if needed.