Storage bridges are an indispensable part of today's computing ecosystem. Internal ones may enable different I/O ports in a motherboard, while external ones are responsible for a variety of direct-attached storage units. These may range from low-performance flash drives with an USB interface to full-blown RAID towers interfacing over high-performance links such as Thunderbolt 3. While Thunderbolt 3 remains a premium Intel-only interface for now, USB 3.1 Gen 2 has emerged as a mass-market high-performance alternative. It is available across systems based on chipsets from multiple vendors. In this context, high-speed USB 3.1 Gen 2 storage bridges are interesting to analyze. Today, we look at Plugable's USBC-NVME NVMe SSD enclosure that bridges a PCIe NVMe device (M.2 2280 or smaller) to a USB 3.1 Gen 2 Type-C interface.

Introduction

High-performance bus-powered USB 3.1 Gen 2 storage devices have traditionally belonged to one of two categories - a SATA SSD behind a USB - SATA bridge, or, a couple of SATA SSDs behind a USB-to-dual-SATA RAID bridge. The first category is still bottlenecked by the SATA interface, and typically delivers 500 - 550 MBps of throughput. The second category can come close to saturating the USB 3.1 Gen 2 interface. However, it depends heavily on the workload type. In order to consistently take advantage of the interface across a variety of workloads, it is necessary to place a PCIe 3.0 x2 or better NVMe SSD behind the USB interface. Bridges with this feature were introduced by JMicron and ASMedia at Computex 2018. We have already reviewed the MyDigitalSSD M2X M.2 NVMe SSD Enclosure based on the JMicron JMS583 bridge.

The Plugable USBC-NVME enclosure we are looking at today is also based on the same bridge chip. It can accommodate a M.2 2230 / 2242 / 2260 / 2280 NVMe SSD. The aluminum enclosure comes with two 25cm cables - a Type-C to Type-C, and a Type-C to Type-A . Both are rated for 10 Gbps operation. Plugable also supplies three thermal pads, and rubber pegs (one for each supported M.2 SSD size).

The SSD can be installed in a tool-free manner since the casing is fastened to the bridge-chip-bearing frame by a spring-loading mechanism. The installed M.2 SSD is held in place by the aforementioned rubber peg. We put in a MyDigitalSSD SBX 1TB PCIe 3.0 x2 NVMe SSD for performance evaluation. Note that this is the same SSD that was used to evaluate the MyDigitalSSD M2X enclosure.

In the rest of this review, we compare the Plugable USBC-NVME with a host of other storage bridges (including the TEKQ Rapide Thunderbolt 3 enclosure). Note that only the MyDigitalSSD M2X belongs to the same specific category as the Plugable USBC-NVME. The table below presents the detailed specifications and miscellaneous aspects of the units and how they compare.

Power Consumption - CrystalDiskMark
Plugable USBC-NVME - JHL6540Plugable USBC-NVME - ASM2142Plugable USBC-NVME - CNP-LP PCHSatechi B01FWT2N3KTEKQ RapideCRU ToughTech Duo C - RAID 0MyDigitalSSD M2X - USB 3.1StarTech.com S251BU31C3CBCRU ToughTech Duo C - RAID 1Axtremex Micro SSD Gen2	Plugable USBC-NVME - ASM2142Plugable USBC-NVME - CNP-LP PCHSatechi B01FWT2N3KTEKQ RapideCRU ToughTech Duo C - RAID 0MyDigitalSSD M2X - USB 3.1StarTech.com S251BU31C3CBCRU ToughTech Duo C - RAID 1Axtremex Micro SSD Gen2Plugable USBC-NVME - JHL6540

Any difference in power consumption for the same access trace between two different units is down to the storage bridge itself (since the drive used is the same in all cases). Peak power consumption for the USBC-NVME with the JHL6540 and the ASM2142 was around 4.8W (same as the MyDigitalSSD M2X). The USBC-NVME idled at around 1.5W on both of our test systems, compared to the 1.2W number for the M2X (albeit, on a different testbed). We can't reliably conclude whether the difference in the host system (our custom Skylake testbed against the Hades Canyon NUC) is responsible for the lower idle power of the M2X, as it is also possible for the bridge firmware to be slightly different between the M2X and the USBC-NVME.

Miscellaneous Aspects and Concluding Remarks

SATA - USB storage bridges that support UASP fully can translate the SCSI UNMAP command to TRIM commands for SSDs connected to the downstream port. In the case of M.2 NVMe - USB storage bridges, the bridge chip has to recognize the corresponding NVMe command and pass it downstream appropriately.

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 H -ReTrim -Verbose (assuming that the drive connected to the storage bridge is mounted with the drive letter H)
• Re-execute trimcheck to determine status report

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

We find TRIM working in the Plugable USBC-NVME with the MyDigitalSSD SBX 1TB SSD, as expected.

Our evaluation of the Plugable USBC-NVME had two aspects - the comparison of different USB 3.1 Gen 2 hosts currently in the market, and the comparison of the product itself against the MyDigitalSSD M2X enclosure. Our benchmark numbers have shown that the ASMedia ASM2142 and the Cannon Point-LP PCH's implementation of the USB 3.1 Gen 2 perform very similar to each other. Alpine Ridge / JHL6540 turned out to be an also-ran. To its defense, the DHL6540 / JHL6540 controllers have been around for more than a couple of years now. Evaluation of the newer Titan Ridge controller for similar workloads may yield numbers similar to what we obtained for the ASM2142 and CNP-LP PCH.

The Plugable USBC-NVME is perfect for consumers who need to mount and dismount M.2 NVMe SSDs frequently. An example would be a scenario where a user needs to quickly identify the contents in a M.2 NVMe SSD prior to formatting for installation in a PC. The tool-less aspect is a major contributor to this aspect. The downside is that the thermal performance is not as good as that of the MyDigitalSSD M2X.The M2X is more suitable for use-cases where the installed SSD needs to be swapped out very rarely. Despite using the same bridge chip (JMicron JMS583), the enclosures excel for different use-cases.

As of the time of posting this review, Plugable has sold out of their initial stock of the USBC-NVME enclosure. The next shipment is on the way, and should be available again on Amazon for USD 50 shortly. The pricing is a bit higher than the USD 40 for the MyDigitalSSD M2X. Consumers can go in for either enclosure based on their intended use-case.