Slightly off topic, but figured it would be worth documenting. I’ve noticed that model from Acasis, and while they don’t provide the technical details, something seems off to me. They specifically state that one drive only gets 1500MB/s:
Measured speed: It can reach 2800 MB/s with a RAID 0 setup, and normally each SSD transfers at about 1500 MB/s.
The single drive enclosure I have (TBU405) with a WD Black SN850 2TB already gets ~2800 MB/s speed (see attached speed test I just ran). Both have the same controller, JHL7440. So for the same controller with a single drive to get slower speeds in the 2-bay enclosure, I’m guessing that there are less PCI lanes per M.2 drive, probably half of what the JHL7440 supports, so that two drives are required to get the full speed. OWC did something similar in one of their multi-slot M.2 enclosures, and it took a lot of digging to figure out they had limited lanes to each drive.
So the two bay enclosure only makes sense to me if you want to mirror (Raid 1) or need more capacity than the largest M.2 drives currently available*. The Acasis 2 bay enclosure does not do the raid itself, it’s using OS provided software raid as they state on the product page.
*You could technically use two separate one drive enclosures and use Disk Utility to stripe (raid 0) then into a single volume, but not sure what would happen if you only attached one (suspect bad, hopefully not mount). You should get faster read times since data could be read from both drives at the same time, maybe ~4000MB/s? Total guess, but based off the Acasis increase from 1500 to 2800 seems reasonable. TB4 max theoretical throughput is 5000MB/s (40Gbps).