OWC Express 4M2 review: Four SSDs are better than one

The OWC Express 4M2 is a fast Thunderbolt 3 enclosure that allows you to leverage up to four NVMe SSDs for large amounts of performance-oriented external storage. This can be as individual drives/volumes, or amalgamated in RAID. (You need to supply your own NVMe SSD modules.)

That’s nicely versatile, but RAID is what you should buy the Express 4M2 for. Its non-RAID, single-SSD performance was disappointing, however.

OWC Express 4M2: Features and specs

The Express 4M2 is a Thunderbolt 3 enclosure with two Thunderbolt 3 ports as well as a full-sized DisplayPort port. That’s a bit of a giveaway to the unit’s older design. Inside, there are four M.2 slots supporting PCIe 3.0–another giveaway.

OWC’s website doesn’t cite any limitations on the capacity of the SSDs you can install, so at the moment, you can likely stuff this thing to the tune of 32TB.

The enclosure measures just shy of 2.5 inches tall (rubber feet included), a little over 4.5 inches deep, and almost 5.4 inches wide. There’s a rather large fan that you must remove to install SSDs (our test unit was unpopulated), but it’s an easy deal, and said fan is very quiet.

As you might guess, an AC adapter is required to power four SSDs. In this case, a hefty 6-amp, 12-volt unit with a coax connector on the drive end, and a removable three-prong cable on the other.

OWC might’ve been better off renaming the Express 4M2 after the introduction of its much faster, far more versatile (and pricier) Express 1M2 cousin. As the Express 1M2 is USB 4, it’s a bit of a confusing marketing message.

To operate the Express 4M2 in RAID, you need software. OWC provides a license for its handy cross-platform SoftRAID, though the Pro portion that allows you to create volumes expires three years from the date of purchase. SoftRAID remains functional–including the ability to rebuild in case of drive failure–perpetually.

You can also leverage macOS or Windows RAID to the same effect, though that kills any cross-platform use. Platform agnosticism is one of the reasons I’m still a fan of hardware RAID.

OWC Express 4M2: Speed and performamce

As I’ve already stated, the Express 4M2’s performance varies by drive configuration, but all told, it’s a very fast reader and a fast writer–depending on what you compare it to.

It’s not fast compared to the Express 1M2, which proved fast across every bus we tried (5Gbps USB to 40Gbps USB 4/Thunderbolt). We included the 1M2 results to show you just how much you’re missing.

We tested on a Mac Studio with Disk Speed Test and AmorphousDiskMark, but we also tested using sister publication PCWorld’s test bed and suite. On both platforms, we tested the unit as four single 2TB SSDs (testing one), a single 8TB volume in striped RAID 0, and a single 4TB volume in RAID 1 + 0.

Four 2TB, PCIe 4.0 NVMe SSDs were employed–each easily capable of 5GBps reads and 4GB writes. The results surprised us a bit.

It was the single-drive performance that really shocked us. This is a PCIe 4.0 NVMe SSD which is easily capable of outpacing 40Gbps Thunderbolt 3. I can’t say for sure, but the bandwidth is likely split evenly across the four slots, leaving only 10Gbps to play with. That’s what the results read like.

Next up are the PCWorld test results, which largely agree with the macOS testing–fast in RAID 0, fast with slower writing in RAID 1 + 0, and below-average performance in non-RAID mode.

Note that to get top performance under Windows (tested for the charts), we had to specifically set the Express 4M2’s properties/policy (the SoftRAID software warns you about this) to Best performance or write speed in both RAID modes was halved.

CrystalDiskMark 8 Read performance was outstanding in RAID 0, and fantastic in RAID 1 + 0. RAID write performance was good, but as you can see from the 1M2 and Sandisk Pro-G40, hardly outstanding.

Again, the very weak performance using only a single SSD indicates a partial bandwidth allotment. It’s faster than a hard drive to be sure, but if you’re looking to add four separate volumes, you’ll be much better off with single-drive enclosures. Unless of course, you’re out of ports–few single SSD enclosures offer pass-thru.

CrystalDiskMark 8 rated random performance as good, and this is the one area where the Express 4M2 in non-RAID mode kept up.

Our real-world 48GB transfers mimic the CrystalDiskMark 8 conclusion. RAID 0 is best, RAID 1 + 0 next, and single SSD mode the worst.

We’re not sure why RAID 1 + 0 is so slow writing as there are still two volumes to shotgun writes across, but keep in mind that this is software RAID that’s at the mercy of your computer’s CPU. The RAID 0 450GB write time is good for an external drive. The RAID 1 + 0 and single drive times are not.

In total, we found the Express 4M2 delivered the read and write speeds you’re looking for in RAID 0, the read speed in RAID 0 + 1, but rather weak reading and writing in single drive mode. Additionally, the 4M2 ran very cool in our testing–lots of internal air and the fan saw to that.

Caveat: RAID 0 offers no fault tolerance. As reliable as modern NVMe SSDs have proven, if one goes bad, you’ll lose all your data. We don’t know how much recovery for an SSD RAID setup would cost, but it’s unlikely to be cheap, even if it is possible.

Should you buy the OWC Express 4M2?

If you plan to fully populate the Express 4M2 in RAID 0, go for it. The performance will largely live up to expectations. Other modes, not so much. Again, you might be better off with multiple single drives such as OWC’s outstanding, fast, and super versatile Express 1M2.