Storage bridges come in many varieties within the internal and external market segments. On the external side, they usually have one or more downstream SATA ports. The most popular uplink port is some sort of USB connection. Within the USB storage bridge market, device vendors have multiple opportunities to tune their product design for specific use-cases.

Today's review will take a look at TerraMaster's D2-310, a 2-bay direct-attached storage device. It can accommodate either 2.5" or 3.5" drives, and connects to the computer using a USB 3.1 Gen 2 Type-C port. It is externally powered using a 40W adapter. A Type-C to Type-A cable is bundled with the unit. Screws for installing both 2.5" and 3.5" drives are supplied.

Almost all multi-bay direct-attached storage devices come with hardware RAID. The D2-310 is no different. Internally, the product uses the ASMedia ASM1352R to bridge the two SATA ports to a USB 3.1 Gen 2 port. The bridge chip also comes with hardware RAID capabilities, and the D2-310 has a rotary switch in the rear panel (near the Type-C port) to select the required configuration. The device doesn't need to be power cycled when the RAID configuration is changed by the user. Instead, the 'Reset' button needs to be pressed for 5 seconds in order to create a new RAID volume with the selected configuration. Tools for attaching the drives as well as modifying the rotary switch position and activating the reset button are provided in the accessory package.

Consumers need to keep the following aspects in mind for external storage devices / enclosures with a USB interface:

• Support for UASP (USB-attached SCSI protocol) for better performance (reduced protocol overhead and support for SATA Native Command Queueing (NCQ))
• Support for TRIM to ensure SSDs in the external enclosure can operate optimally in the long run
• Support for S.M.A.R.T passthrough to enable monitoring of the internal SATA device by the host OS

In the rest of the review, we evaluate the above aspects and also look into the performance of the unit.

The table below presents the detailed specifications and miscellaneous aspects of the units and how they compare.

Our evaluation routine for storage bridges borrows heavily from the testing methodology for direct-attached storage devices. The testbed hardware is reused. CrystalDiskMark is used for a quick overview, as it helps determine availability of UASP support and provides some performance numbers under ideal scenarios. Real-world performance testing is done with our custom test suite involving robocopy bencharks and PCMark 8's storage bench.

Performance with SSDs

Storage bridges operate in the maximum possible performance mode when the storage media is able to saturate the SATA links. SSDs are best suited for this purpose. Our first set of tests help in understanding how the TerraMaster D2-310 behaves with Crucial MX200 500GB SSDs in the drive bays.

CrystalDiskMark uses four different access traces for reads and writes over a configurable region size. Two of the traces are sequential accesses, while two are 4K rando accesses. Internally, CrystalDiskMark uses the Microsoft DiskSpd storage testing tool. The 'Seq Q32T1' sequential traces use 128K block size with a queue depth of 32 from a single thread, while the '4K Q32T1' ones do random 4K accesses with the same queue and thread configurations. The plain 'Seq' traces use a 1MiB block size. The plain '4K' ones are similar to the '4K Q32T1' except that only a single queue and single thread are used.

Comparing the '4K Q32T1' and '4K' numbers can quickly tell us whether the storage device supports NCQ (native command queuing) / UASP (USB-attached SCSI protocol). If the numbers for the two access traces are in the same ballpark, NCQ / UASP is not supported. This assumes that the host port / drivers on the PC support UASP. We can see that the TerraMaster D2-310 supports UASP. The bridge is also able to sustain as much as 685 MBps for certain workloads.

Power Consumption - CrystalDiskMark Workloads
TerraMaster D2-310 - RAID 0TerraMaster D2-310 - RAID 1	TerraMaster D2-310 - RAID 1

Performance with Hard Drives

The benchmarks processed in the previous section were also run with two WD Red 8TB hard drives in the unit. Running the robocopy benchmarks segment of the AnandTech DAS Suite with hard drives attached to the storage bridge gives us the following performance numbers. The graphs show that the storage bridge is able to sustain around 350 MBps for sequential workloads when modern-day high-capacity consumer hard drives are used.

Power Consumption - CrystalDiskMark Workloads
TerraMaster D2-310 - RAID 0TerraMaster D2-310 - RAID 1	TerraMaster D2-310 - RAID 1TerraMaster D2-310 - RAID 0

Miscellaneous Aspects and Concluding Remarks

The TerraMaster D2-310 allows for hot-swapping of drives. That essentially means that the unit is able to tolerate sudden failure of one of the drives, and also rebuilds automatically once a new drive of equal or large capacity replaces the failed drive. We tested this aspect by playing back a video from a file stored in a RAID-1 volume (2x Crucial MX200 500GB) and yanking out one of the drives during the operation. There was no visible impact on the playback, while the LED corresponding to the missing drive started blinking red in the front panel.

RAID Rebuild

Rebuild was evaluated by using another Crucial MX200 500GB SSD to replace the one that was yanked out. The LED blinking red turned into blinking amber. For the first 20 - 30 seconds, we made sure that the video playback continued smoothly while the RAID rebuild started. After that, we stopped the video playback, and let the rebuild operation complete at full speed. The unit was connected to the PC throughout the process. Completion was signaled by the amber blinking LED turning solid green. We tracked the power consumption at the wall during the process.

The rebuild process took around 16.5 minutes (992 seconds, to be exact), and the at-wall power consumption stayed around 10.5 W throughout. The above graph also shows the power consumption dropping to around 3.2 W with only a single SSD in the unit.

TRIM Support

Storage bridges that support UASP fully can translate the SCSI UNMAP command to TRIM commands for SSDs connected to the downstream port. Checking for TRIM support has been a bit tricky so far. CyberShadow's trimcheck is a quick tool to get the status of TRIM support. However, it presents a couple of challenges: it sometimes returns INDETERMINATE after processing, and, in case TRIM comes back as NOT WORKING or not kicked in yet, it is not clear whether the blame lies with the OS / file system or the storage controller / bridge chip or the SSD itself. In order to get a clear idea, our TRIM check routine adopts the following strategy:

• Format the SSD in NTFS
• Load the trimcheck program into it and execute
• Use the PowerShell command Optimize-Volume -DriveLetter Z -ReTrim -Verbose (assuming that the drive connected to the storage bridge is mounted with the drive letter Z)
• Re-execute trimcheck to determine status report

Conclusions can be made based on the results from the last two steps.

Unfortunately, the TerraMaster D2-310 does not support TRIM passthrough. With its focus on 3.5" drives, the absence of the feature can be excused.

Final Words

The TerraMaster D2-310 is a solid 2-bay direct-attached storage unit. It is novice-friendly, and all the tools needed for operation are provided in the package (including a screwdrive to secure the drive to the bays). The enclosure's industrial design is pleasing to the eye, and the performance meets expectations.

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In terms of scope for improvement, TerraMaster could include a better power adapter (the wire between the adapter and the unit does not inspire much confidence - a contrast to the rest of the parts that appear to be on the higher end of the quality scale). It would also be good if TerraMaster adopts industry-standard terminology for the RAID levels - the SINGLE setting in the unit actually corresponds to JBOD, while the JBOD setting corresponds to SPAN. The fan used for cooling is pretty quiet (subjectively speaking), but, it would be nice to have a switch to turn it off completely (in case SSDs are being used). This is a feature available in similar units from TerraMaster's competitors.

​The TerraMaster D2-310 is available on Amazon for $160. Cheaper units are available, but, consumers looking for something with the style and build quality of the D2-310 will find the pricing par for the course.