Many of us have more USB4 and Thunderbolt devices than our Macs have ports. In my case, I need to have four external NVMe SSDs connected to my Mac mini M4 Pro with its three ports, one of which is already committed to its Studio Display. One solution is a Thunderbolt 4 hub, but those tend to come with only three ports, so I’d need to connect two, either to both the free ports or in a daisychain from one. This article considers an alternative: OWC’s four-bay Express 4M2 enclosure.

The original 4M2 supported Thunderbolt rather than USB4. When used as a RAID array, with SoftRAID, it delivered excellent performance, but as a plain four-bay enclosure for separate disks it was slow and only delivered about 800 MB/s. The current version now supports USB4, and gives each bay a single lane of PCIe 4.0. I have just completed testing my new 4M2 with three Samsung 990 Pro 2 TB SSDs, connected to my Mac mini M4 Pro. Results given here are for the ‘gold standard’ test using Stibium.

Transfer speeds without RAID are limited to just over 1.6 GB/s for both read and write, but are sustained at that even when reading or writing simultaneously to two of its SSDs. Simultaneous transfers to three or four SSDs will reduced, though, as the total then exceeds the 3.2 GB/s available through its single USB4 connection to the host Mac. A future model could perhaps use the full four lanes over Thunderbolt 5, but that’s unlikely this year and will inevitably be more expensive.

The speed of the 4M2 is remarkably consistent compared to those delivered in practice by hubs or docks. At their best they can almost match a direct connection, but sometimes they can be surprisingly slow for no apparent reason.

As expected, the enclosure is beautifully engineered in aluminium, and has internal heat sinks to variable-speed fans that are far more protective than anything available in single-SSD enclosures. Although a little larger than a Mac mini, it isn’t overpowering, and looks petite alongside a Mac Studio.

There’s considerable cost saving to be achieved as well. The 4M2 typically sells for around $/€/£ 240. Single OWC Express 1M2 40G (USB4) enclosures cost half that, so four would come to about $/€/£ 480, to which you’d need to add two TB4/USB4 hubs, for a total of $/€/£ 880.

If you can live with a consistent 1.6 GB/s, or want the substantially better performance available with RAID, the OWC 4M2 is the best choice for connecting multiple NVMe SSDs to the minimum number of ports on your Mac.

OWC’s product page is here.

In case you’re wondering, I paid full price for my 4M2 from an Amazon Marketplace vendor in the UK.