Hardware RAID 0, 1, concatenated and single drive mode
Noisy fan on our test unit
UGreen’s CM335 is a good performer and one of the more affordable dual-bay 3.5-inch hardware RAID boxes on the market.
Established Mac-centric vendors have recently abandoned hardware RAID for the more versatile but CPU-cycle-stealing software variant. Hence our interest in UGreen’s CM335 hardware RAID enclosure, which tips the money scale at a slim $149, yet doesn’t tax your computer’s CPU while it goes about its business. It’s a good performer, although it does require high-quality cables.
Design and features
The CM335 is cheap for what it is, although it sometimes shows. The construction is entirely plastic, but still manages to create a reasonably elegant profile on the desk. Being largely plastic also makes it light at about five pounds, even though it’s 8.4 inches deep, by 5.3 inches wide, by 5.7 inches (all approximate measurements).
But the lack of heft can also translate into a somewhat unsubstantial feel, at least if you fill it with 2.5-inch SSDs or HDDs. Considerably heavier 3.5-inch hard drives add gravity that might otherwise be missing.
On the front of the enclosure are the status lights (power/drive activity) and drive bays with non-locking, lift-handle, plastic push-fit trays. The trays use quick-fit, removable plastic mounting rails (long tabs with pins that fit into the hard drive’s screw holes).
You’ll need to remove one of the rails to mount a 2.5-inch drive, as the front pin prevents proper alignment. Keep the rails around as they are very handy for quickly installing HDDs should you ever need to switch. With 2.5-inch media installed, there’s plenty of room inside the drive bay to stash them away.
UGreen thoughtfully provides enough screws for four drives (there are only two bays) as well as a small screwdriver should you be short. Nice touch. Tip: I have found that using a soft pencil on the contact areas of plastic joints works well as a non-greasy lubricant.
On the back of the CM335 is the power connector (a 1.2 amp/12 volt adapter is included), instant on/off button, recessed reset button, single USB Type-C port (5 Gbps) and the dual dip switch , used to configure RAID mode. The options are RAID 0 (striped/fastest), RAID 1 (mirrored/single drive speed), Span (chained), and PM (Port Multiple), which treats the two drives as separate logical units.
The dip switch is a dead giveaway that the box is hardware RAID. i.e. The RAID is handled on board by a controller chip. We’ve seen a lot of newer enclosures (even smaller two- and four-drive units) that rely on the operating system to provide RAID functionality. Software RAID is more versatile when you have more than two drives, but also tends to reduce performance under heavy load.
On a dedicated file server, software RAID like that offered by ZFS, UnRAID, etc. is fine, and actually preferable. However, on a client computer performing a variety of other CPU-intensive tasks, it is less than ideal under heavy load.
Being USB 5Gbps, the UGreen theoretically has plenty of bandwidth for both SATA HDDs and SSDs – around 550MBps sequential throughput under optimal circumstances. The CM335 came close to that (about 470 MBps on the PCWorld storage test bed) in our tests with two SSDs operating individually as well as in RAID 1.
In comparison, TerraMaster’s d2-310 managed 510 MBps in RAID 0. For some reason, as you’ll see below, the CM335’s read performance with SSDs actually suffered somewhat under RAID 0, and there wasn’t the usual jump in write speed that was offered by splitting/striping data across two drives.
The results on my 2015 iMac were lower than on PCWorld’s test bed, but that’s almost always the case with USB storage; 320 to 370 MBps is a good number for testing on my machine. You can do better on a newer Mac, but not by much. For some reason Macs don’t work that easily with USB.
Since the CM335 is a very good fit for hard drives, I also tested with two 12TB HDDs in both RAID 1 and 0. In RAID 0, the box is almost as fast as it was with SSDs in terms of sequential throughput, however with relatively pathetic search and performance for small files. The nature of the beast. Regardless, there’s something about seeing a 24TB logical drive on my desktop that’s still impressive.
Blackmagicdesign’s Disk Speed Test only tests sequential throughput, which was quite good with the CM335, even with hard drives as shown below. Note that these were top-of-the-line WD and Seagate HDDs.
I have to warn you to use the top quality cable provided by UGreen or another of a similar nature. Performance dropped sharply to 35 to 40 MBps with longer, thinner (and cheaper) USB cables. I’m just warning you so you don’t freak out if you see these dull numbers using a cable you might already have connected.
AmorphousDiskMark (a CrystalDiskMark port for Mac) tests random, small file operations, which are always much slower with hard drives that have to move a read/write head around platters. Compare the RND4K numbers with those in the CrystalDiskMark 8/PC image at the top of this section to see how much slower HDD small file transfers are than an SSD’s.
All in all, the CM335’s performance was very good, although the lower RAID 0 read performance was a bit of a puzzle. Considering the price, we consider it a minor weakness.
Our test unit suffered from a noisy fan bearing. UGreen seemed surprised by the issue, so we’re assuming a one-off defect or shipping damage. There is a 30-day return policy if you buy the CM335 on Amazon, which is actually the only place I’ve seen it for sale.
A good performance purchase
The CM335 is decently fast, affordable, easy to set up and, despite its all-plastic construction, doesn’t look out of place sitting next to or behind a Mac. A good solid storage box at a reasonable price.