For my storage needs, my first NAS was a Synology DS415+. This was my primary NAS until I purchased a DS1618+, at which time it became my backup unit. When I filled up the DS1618+, I had a few options: buy a small NAS and use some 4TB disks I had on hand, or buy bigger disks, or buy a NAS with more storage bays. I chose to buy a DS220+, into which I shoved two 4TB drives, and this became a second primary onsite unit.
A couple weeks ago, the DS415+ died, leaving me with no local backup. (I have a DS118 offsite at a friend's house, which is used as one of my two offsite backup targets.) I purchased a DS1821+ as a new primary system, and the DS1618+ became my local backup unit. All of my NASes are set up for SHR (primary is SHR2), and all of my NAS transitions have been as seamless as one would expect from Synology: the process was as simple as: move the drives, (re)install the OS, and go.
I will be selling the DS220+ soon, because I have added yet another spare 4TB drive to the DS1821+, and am in the process of relocating data from the 220 to the 1821. This also frees up the two 4TB drives that were in the DS220+, and those will go into the other two NAS units.
I never like losing a NAS, but it's nice that this worked as well as one could hope. As a bonus, I got an upgrade to the latest offering from Synology, which also allows me to free up another drive bay: I can switch from SSD cache to NVMe cache -- when I buy an NVMe drive or two.
I am a system engineer in the Raleigh, NC area. My main interests are Unix, VMware, and networking. More about me, and how I got started.