As it so happens, I make SSDs for a living.
For a single user environment, network attached SSDs are a waste. Network attach works well when there’s a high duty cycle workload. Single user workloads are mostly idle time. The latency over the network will wipe out most of the gains you would expect to see from an SSD. And even if you’re running 1Gb network connections, that’s only around 100MB/S. HDD speed. A single SSD is going to be 5x faster than that, minimum. Network storage for single user workloads is still best implemented with HDDs (and you can buy a 10TB HDD for about $100).
You want a direct-attach solution for your SSDs.
Flash memory is a consumable media, it wears out with use. SSDs have a physical capacity which is often greater than the logical capacity. The extra memory is called “over provisioning” and it’s used to improve write performance and increase endurance. For example, a drive with 256GB of raw memory would report 240GB of logical capacity and be said to be “7% over provisioned”. The “256GB” logical capacity point means these drives don’t have a lot of over provisioning, which means that they’re not high endurance drives. Also means their write performance probably won’t be that stellar. But if they’re year old low-over-provisioned drives, depending on how they were used they could have an appreciable amount of wear (meaning their remaining life is going to be shorter). If you poke around on the Internet, you can probably find a tool from the SSD manufacturer that you can use to see how worn out the drives are (it’ll be expressed as a percent).
Assuming they all have about the same life used percentage, I would take the drives and RAID them. RAID-5 if you can find a controller that supports it. An array of 7 drives would give you 1.5TB, give you fault tolerance for a single drive failure, give you read and write performance that’s going to scale close to linearly as a function of drive count (meaning it’ll be about 6 times faster than a single drive). Keep one drive as a spare. This will spread the write activity uniformly across the drives, which will also extend the endurance. If each drive in the array has 1 year of life left, 6 drives would give you 6 years at the same level of writing.
If you can’t do RAID-5, then shoot for RAID 1+0 (a mirrored 4x drive stripe set), it’ll give you 4x performance (if the controller is smart enough, it could actually give you 8x performance on reads) and 1TB total capacity with redundancy. Any external box with Thunderbolt should be able to keep up with the speed of the SSDs. A lot of them do RAID 0+1.
You want redundancy. SSDs are a heck of a lot more reliable than HDDs, but the more of them (anything, for that matter) you are using the greater the odds you’ll have one will fail. RAID is the best way to protect yourself from the inevitable. When a drive in a RAID fails, the array continues to function with no data loss, but in a “degraded” state (where the loss of an additional drive will result in data loss). But when you put a new drive in to replace the failure the array becomes fault tolerant again. Theoretically, as long as you’re there to replace drives when they fail, the data on a RAID array will last forever, no matter how many drives fail (as long as they only fail one at a time).
Are you sure the drives are SATA and not NVMe? One year old systems, I’d expect m.2 NVMe.
My home system has 10x SSDs. A 3.2TB RAID-5 (3x 1.6TB 12G SAS drives), a 1.6TB RAID-5 (5x 400GB 6G SATA drives) and two stand-alone 400GB SATA drives that I use as scratch disks. The RAIDs are handled by an LSI Logic 9260 PCIe Gen3 controller. The motherboard is a SandyBridge and it does a decent job of handling the stand-alone drives. The system is actually getting a bit “long in the tooth” I built it about 6 years ago. But it still delivers quite respectable transfer rates to the RAIDs up in the 1.5GB/S range. Every time I think about upgrading, I ask myself “why?” and then I don’t. I could build something faster but it’d only matter to the benchmarks, I wouldn’t notice…
Unfortunately, I can’t give you a lot of advice about Mac. But I can tell you almost anything you want to know about SSDs and storage arrays.