I have 3 Netgear ReadyNAS units, which I have acquired over the last 15 years or so. And are just for storage serving purposes.
The oldest, a low powered Duo, is limited to 2TB drives, which I run in RAID1.
The other two are also 2-bay units with Intel Atom processors with more memory. Both have dual Gigabit connections, in adaptive load balancing mode (from the ReadyNAS Pro models)
One, a Ultra Plus, is my main NAS with 2 x 10TB drives in RAID1
The other, a Ultra, is for backup, running 2 x 8TB in RAID1 also.
There are scheduled backup jobs running from the Main NAS to the Backup units.
So my 8TB music library is mirrored over 4 disks.
I also have a 12 TB RAID0 volume in a USB enclosure, which provides an ‘offline’ backup.
I have a couple of single USB disks, so other data is backed up and mirrored over 3 disks.
The separate 2-bay units give resilience with independent back plane, power supplies, networking etc.
All units are on a UPS to protect against mains power issues.
I would have run LMS on a NAS when I started streaming ‘08/‘09, but moved to Asset on a dedicated RPi2, and then to Roon on NUC, running ROCK.
I also run volume comparison checks to ensure the backups are copies of the master version.
I would not look to build a NAS DIY as the commercial products are good, the firmware/software is proven, easy to use and reliable.