I have a Synology single drive NAS it works great (OK CPU is underpowered). I have primary copy on my PC. Second copy on NAS. And NAS backs up to cloud (AWS Glacier). Multiple drive NAS have the redundancy and speed but I really dont need that, the single drive is cheaper. Every few years I'll upgrade PC drive and give my old HD to my Dad as a just in case backup.

Great question: it's for expandability.

If you run RAID-1 in a 2-slot NAS, and you run out of space, you've got two options:

1) buy another NAS

2) move off of RAID, and have 2 distinct volumes. You'll have twice the storage, but no spindle redundancy.

If you've got 4 or 5 slots, you can throw in 2 larger disks, and use the prior disks either for backup, or use the new disks for incremental additional storage. You've just got a ton more flexibility.

So you are just recommending a NAS with at least 4 drive bays, not necessarily 4 drives, I read this and interpreted it as 4 drive minimum for data redundancy:

"Consider getting a NAS that has 4 or more drives to offer redundancy and support data integrity checks"

I may go for a 4 bay, but I never upgraded capacity in the last 7 years (3TB mirrored) and would probably go 14TB mirrored on the new one, so seems like a waste.

> I never upgraded capacity in the last 7 years (3TB mirrored) and would probably go 14TB mirrored on the new one, so seems like a waste.

Wow, yeah, if your storage growth is that stable, and there's a big cost penalty for 4+ slots, then a 2 slot NAS would seem like a good idea.

Yeah movie collection not growing, thats all streaming now, for new stuff. Photos in iCloud so on multiple devices, but may go to Synology backup with new one. Documents are nothing.

Main thing I will use more capacity for will be more surveillance camera footage retention and more and higher res cameras.

Ah crap that should say slots, not drives, my bad. Thanks for bringing this to my attention!