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. eSATA as an uplink interface is on the way out. High-end products have Thunderbolt support. 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 the S251BU31C3CB and the Satechi B01FWT2N3K. Both of them are USB 3.1 Gen 2 Type-C enclosures for 2.5" SATA drives with a metallic exterior. There are some subtle differences between the two - the unit has the Type-C cable integrated, and the chassis is designed to be able to stow away that cable for easy portability. The Satechi unit has a Type-C cable included in the package. Consumers interested in the aesthetics aspects might also find the Satechi unit attractive, as it comes in three different colors - Space Gray, Gold and Silver.

Both the units come with a screwdriver and appropriate screws. The unit has screw mounts for the 2.5" drive to the internal plastic bay, and the bay to the metal chassis. The Satechi unit has screw mounts only for the bay to the metal chassis (and it comes pre-installed, as can be seen in the above gallery). The pictures in the gallery also show that the unit uses the ASMedia ASM1351 bridge chip, while the Satechi unit uses the VIA Labs VL716 bridge chip.

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

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. We use the Crucial MX200 500GB SSD as the storage drive for all the bridges / enclosures that we are evaluating as part of this review series.

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

Comparative Storage Bridges Configurations
Downstream Port 1x SATA III 1x SATA III
Upstream Port USB 3.1 Gen 2 Type-C USB 3.1 Gen 2 Type-C
Bridge Chip VIA Labs VL716 ASMedia ASM1351
Power Bus Powered Bus Powered
Use Case 2.5" HDD/SSD Enclosure (up to 9 mm height) with Female Type-C Interface 2.5" HDD/SSD Enclosure (up to 9 mm height) with Integrated Type-C Cable
Physical Dimensions 127 mm x 81 mm x 13 mm 140 mm x 85 mm x 14 mm
Weight (diskless) 118 grams (with cable) 126 grams
Cable 29 cm USB 3.1 Gen 2 Type-C (Male to Male) 27 cm Integrated USB 3.1 Gen 2 Type-C Cable (Male)
S.M.A.R.T Passthrough Yes Yes
UASP Support Yes Yes
TRIM Passthrough Yes Yes
Price USD 30 USD 35
Review Link Satechi B01FWT2N3K Review S251BU31C3CB Review

Performance Benchmarks

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 NCQ/UASP is supported by both enclosures as the 4KQ32T1 numbers are more than 8x and 3x of the 4KQ1 read and write numbers respectively.

Storage Bridge Benchmarks - CrystalDiskMark

Moving on to the real-world benchmarks, we first look at the results from our custom robocopy test. In this test, we transfer three folders with the following characteristics.

  • Photos: 15.6 GB collection of 4320 photos (RAW as well as JPEGs) in 61 sub-folders
  • Videos: 16.1 GB collection of 244 videos (MP4 as well as MOVs) in 6 sub-folders
  • BR: 10.7 GB Blu-ray folder structure of the IDT Benchmark Blu-ray (the same that we use in our robocopy tests for NAS systems)

The test starts off with the Photos folder in a RAM drive in the testbed. robocopy is used with default arguments to mirror it onto the storage drive under test. The content on the RAM drive is then deleted. robocopy is again used to transfer the content, but, from the storage drive under test to the RAM drive. The first segment gives the write speed, while the second one gives the read speed for the storage device. The segments end with the purge of the contents from the storage device. This process is repeated thrice and the average of all the runs is recorded as the performance number. The same procedure is adopted for the Videos and the BR folders.


Photos Read


High-performance external storage devices can also be used for editing multimedia files directly off the unit. They can also be used as OS-to-go boot drives. Evaluation of this aspect is done using PCMark 8's storage bench. The storage workload involves games as well as multimedia editing applications. The command line version allows us to cherry-pick storage traces to run on a target drive. We chose the following traces.

  • Adobe Photoshop (Light)
  • Adobe Photoshop (Heavy)
  • Adobe After Effects
  • Adobe Illustrator

Usually, PC Mark 8 reports time to complete the trace, but the detailed log report has the read and write bandwidth figures which we present in our performance tables. Note that the bandwidth number reported in the results don't involve idle time compression. Results might appear low, but that is part of the workload characteristic. Note that the same CPU is being used for all configurations. Therefore, comparing the numbers for each trace should be possible across different DAS units.


Adobe Photoshop Light Read

The unit and the Satechi unit perform very similarly in almost all the benchmarks. There are a few traces for which the Satechi performs better, but the unit also has an equal number of access traces for which its performance comes out on top.

Thermal Aspects and Power Consumption

The thermal design of external storage enclosures has now come into focus, as high-speed SSDs and interfaces such as USB 3.1 Gen 2 can easily drive up temperatures. This aspect is an important one, as the last thing that users want to see when copying over, say, 100 GB of data to the drive inside the enclosure, is the transfer rate going to USB 2.0 speeds. In order to identify the effectiveness with which the enclosure can take away heat from the internal drive, we instrumented our robocopy DAS benchmark suite to record various parameters while the robocopy process took place in the background. Internal temperatures can only be gathered for enclosures that support S.M.A.R.T passthrough. Readers can click on the graphs below to view the full-sized version. Between the two enclosure, we find the Satechi one ended up with the SSD at 51C, while the one ended up with the SSD at 55C. That said, there is no issue with overheating or performance consistency in both enclosures.

Storage Enclosure Thermal Characteristics

It is challenging to isolate the power consumption of the storage bridge alone while treating the unit as a black box. In order to study this aspect in a comparative manner, we use the same SSDs (Curcial MX200 500GB) in the units and process the same workloads on them (CrystalDiskMark 5.1.2's benchmark traces with a region size of 8GB and the number of repetitions set to 5). Plugable's USBC-TKEY power delivery sniffer was placed between the host PC and the storage bridge to record the power consumption. The average power consumption for each access trace was recorded. The pictures below present the numbers in a compact and easy to compare manner.

Power Consumption - CrystalDiskMark

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). As we could guess from the temperatre graphs, the unit / ASMedia ASM1351 bridge consumes slightly more power compared to the Satechi unit / VIA Labs VL716 bridge.

Miscellaneous Aspects and Concluding Remarks

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:

  1. Format the SSD in NTFS
  2. Load the trimcheck program into it and execute
  3. 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)
  4. Re-execute trimcheck to determine status report

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

The Satechi unit / VIA Labs VL716 bridge chip has no trouble supporting TRIM for SSDs connected to it. We repeated the same test with the enclosures.

The unit / ASMedia ASM1351 bridge chip has no trouble supporting TRIM. However, we must mention here that we are using a review unit from the latest production batch that has a newer firmware. will be hosting the firmware update for older units on their poduct support page soon.

Coming to the business end of the review, we find that the unit as well as the Satechi unit target slightly different customers. With the choice of colors, the Satechi unit might find wider acceptance with the average consumer. On the other hand, the unit with an integrated cable and a stowing mechanism allows for a more compact and portable unit. The possibility of a missing cable to connect to the PC doesn't arise. However, it also means that users will need an adapter to use with older systems that have only Type-A ports.

For use-cases involving 2.5" hard drives, I would recommend the StarTech unit more because of the extra screws to keep the hard drive mounted to the plastic bay that slides out. The Satechi unit just relies on an elastic pad at the end opposite to the SATA port. Vibration handling could be an issue since the drive might not be mounted snugly in that case. However, this is not an issue for SSDs at all.

Based on our measurements with power consumption for various access traces, the VIA Labs bridge chip appears to be more power efficient compared to the ASMedia one. For use-cases involving notebooks and other battery systems, the Satechi unit with the VIA Labs bridge chip might be preferable.

Both the Satechi and units perform in a similar manner and there is not much difference in the price. We have no hesitation in recommending either unit for purchase, and the reader can opt for the one most relevant to the use-case.

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  • ddriver - Monday, September 26, 2016 - link

    Poor choice of data presentation with the drop down menu selection.... just put them in a chart so people can see how the devices fare over the entire workload range.
  • ganeshts - Monday, September 26, 2016 - link

    (1) Putting in a chart is not amenable to a workflow in which we will compare 4 or more devices (there are a couple more enclosure reviews coming up)

    (2) Putting in separate graphs is an option we have explored for non-pipeline reviews - similar to the section here: ; In a pipeline (single-page) review, the large number of graphs tend to take the focus away from the more important aspects discussed around it.

    All things considered, the drop-down approach will continue to make the best sense for single-page reviews.
  • BrokenCrayons - Monday, September 26, 2016 - link

    Typo on the first line of the second to last paragraph...

    "Based on our measureents with..."
  • ganeshts - Monday, September 26, 2016 - link

    Thanks for the feedback. It has been fixed.
  • DanNeely - Monday, September 26, 2016 - link

    I wonder how much uptake this is likely to see. 2.5" enclosures seem to be getting squeezed out of the middle. For easily pocketable and powerbrick free storage thumb drives are able to do most sneakernet duties these days. On the other end if you're trying to get the most storage for your dollar to largest overall capacity (eg portable backups); nothing's going to top a 3.5" enclosure; and the brick doesn't matter that much for this use.
  • ganeshts - Monday, September 26, 2016 - link

    I sort of agree with your comment, but, I think the market for this is really cheap high-capacity storage / way to reuse existing 2.5" drives that have been decommissioned from computing systems. High-capacity thumb drives carry way too much premium, and also don't support features such as TRIM etc. that can extend the lifetime of the drive.

    To a smaller extent, I believe Windows-to-go installations are much better with these types of devices rather than thumb drives. I have Windows-to-go and portable Ubuntu installs on two different thumb drives (that actually do support TRIM), and the experience hasn't been that good. These enclosures offer a good alternative.
  • tokyojerry - Saturday, October 22, 2016 - link

    Just out of curiosity, does this case support OTG? I think it means 'On The Go'? I am thinking in terms of if I want to attach this to my soon-to-be ZenFone 3 Deluxe (on order) and transfer data back and forth between the ZenFone and a high cap 2TB HDD or SSD. This will also be useful if the soon-to-be-announced Macbook Pros come equipped with USB-C connectors as rumor has it. Thanks.
  • colonelclaw - Monday, September 26, 2016 - link

    On the one hand the integrated cable means you won't lose it, on the other hand, if you break it the unit becomes useless. Choices!
  • Pork@III - Monday, September 26, 2016 - link

    Short cable(27cm vs 29cm) - high speed
  • Cygni - Monday, September 26, 2016 - link

    Would have really liked to have seen the same enclosures running on a 3.0, and even 2.0 interface. Beyond it simply being interesting to see how much 3.1 is helping, most external drives will likely be plugged into the different formats over their lifetime, and different enclosures may handle those lower speeds better.

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