On the other hand, RAID1/5/10 is possible with any of those solutions. They all are software-based in QNAP and Synology NAS devices but also when building your own using mdadm.
And do not forget, RAID does not replace frequent backups.
When buying a ready-to-go NAS you pay for the name and webui. When you're on budget, a Rpi4 build is ok. I was/am running it myself.
Rpi4 has 2 drives connected, (which are WD4TB, SMR drives) and serves the share over NFS to my other Proxmox instance. This instance has VM's which run from the NFS share.
Additionally there is a samba share on the rpi4 for windows clients as a NAS.
It's fine for me. With ext4/RAID1/mdadm still hitting over 100MB/s in each direction
When your drive is SMR-based it may have troubles restoring a degraded ZFS partition
The workaround for bit rotting (which ZFS takes care of) are hashes. Create a cron job, which makes hashes of your files and periodically verify if a hash has changed. Then you know, there is something bad. Create/Verify hashes when making your regular backups.
Or buy yourself a ready-to-go NAS and configure it over the webui you paid for. Many of those products are build on the same platform. The UI differs, and this is overpriced (as I think). I was trying to buy a NAS, but they are so expensive providing only a ARM cpu where you could not even do any VM in.
If you gonna buy a x86 NAS - you will have to expand the RAM and be careful using WD drives in ZFS (ZFS likes also RAM). But for the same model going from ARM to x86 will add like +100$ to the costs of the device.
Therefore I built mine with Rpi4/2GB
https://www.qnap.com/en/product/ts-251+ -- this one is x86/2GB, costs around 350€
https://www.synology.com/en-global/products/DS218 -- this one is ARM/2GB, costs around 250€
WD not ZFS-safe, so take RAID in account
Rpi4/4GB costs around 70€ (with power supply) + external drive cases (~ 2x 30€) + system-software/config (free) = ~130€
Asrock J4105-ITX + RAM + Case & FreeNAS would be also ~200€ project, but you would have up to 4 realiable S-ATA ports.
There are some good HDD cases, like
Fantec DB-AluSky U3 6G 3.5" (8,89cm) USB 3.0 featuring the ASM1051E for example, which can report SMART values, but also power down the HDD and spin in back online. The compatability is there - you just have to know where look for. In case of SMART it's 'smartmontools' or more exaclty 'smartctl'. You can use this tool in your cron jobs to e.g. report values via e-mail. For e-mail you can use postfix. Or skip this all and buy a NAS
What is your usecase,
@Tonyblu331 like: do you work with large files, like 100MB+ or are those many small files?
So yea, there are possibilities.
But I think ready-to-go NAS is more easy to setup / sufficient as they provide built-in S-ATA controller and are more suitable for critical operations.
Here is small benchmark of mine not-that-critical setup, those enclosures I have are running 24/7 and are almost 2 years old: