The internal storage device market segment has seen rapid evolution over the last decade after the introduction of flash-based disk drives. Beginning with 2.5-inch SSDs in early 2010s, the market moved to mSATA units while the SATA-to-NVMe transition started to gather steam. Fast forward to the present, and we find M.2 2280 PCIe 3.0 x4 NVMe SSDs the de-facto standard even for entry-level PCs.

PCIe 4.0 NVMe SSDs are slowly making its way into the market, and many users are finding themselves with spare M.2 SSDs. A common re-purposing method has been to place the SSD in a USB enclosure. Having reviewed multiple storage bridges and enclosures, we have found that companies typically target this market segment with a new product every couple of years (based on the internal drive characteristics going out of fashion / latest USB generation).

Akasa is one of the few manufacturers to possess a SSD enclosure lineup catering to almost all possible scenarios in this market segment. Earlier this year, the company sampled their lineup of M.2 SSD enclosures lineup - the Akasa AK-ENU3M2-02 (SATA), AK-ENU3M2-03 (NVMe), and the AK-ENU3M2-04 (SATA / NVMe) - to put through our storage bridges evaluation routine. All three enclosures come with a USB 3.2 Gen 2 (10 Gbps) host interface. This review takes a look at the performance of each enclosure, their unique aspects, and usage scenarios.

Introduction

SSDs have grown both in storage capacity as well as speeds over the last decade, thanks to rapid advancements in flash technology (including the advent of 3D NAND and NVMe). Starting from 2.5-inch disk drives barely able to saturate the SATA III (6 Gbps) interface in the early 2010s, we now have gumstick- and palm-sized drives with PCIe 4.0 support capable of sustaining more than 7000 MBps (56 Gbps).

These SSDs have also formed the base platform for portable SSDs. Traditionally, such drives have fallen into one of the six categories below, depending on the performance profile and internal components. Recently, we have seen direct flash-to-USB controllers across all but the highest performance tier listed here.

• 2.5GBps+ class: Thunderbolt SSDs with PCIe 3.0 x4 NVMe drives
• 2GBps+ class: USB 3.2 Gen 2x2 SSDs with PCIe 3.0 x4 NVMe drives
• 1GBps+ class: USB 3.2 Gen 2 SSDs with PCIe 3.0 (x4 or x2) NVMe drives
• 500MBps+ class: USB 3.2 Gen 2 SSDs with SATA drives
• 400MBps+ class: USB 3.2 Gen 1 SSDs with SATA drives
• Sub-400MBps+ class: USB 3.2 Gen 1 flash drives with direct flash-to-USB controllers

In addition to portable SSDs, this type of segmentation is also applicable to storage enclosures. Since the mid-2010s, we have seen a regular stream of SSD enclosures hit the market, catering to 2.5-inch, mSATA, and M.2 form-factors.

This review takes a look at three Akasa M.2 SSD enclosures catering to PC users attempting to give new life to their spare SSDs. Irrespective of the M.2 SSD type, Akasa believes that one of the following three enclosures is bound to satisfy the user requirements.

• Akasa AK-ENU3M2-02 : M.2 SATA enclosure with a Type-C female host interface
• Akasa AK-ENU3M2-03 : M.2 NVMe enclosure with a Type-C female host interface
• Akasa AK-ENU3M2-04 : M.2 SATA / NVMe enclosure with Type-A and Type-C male host interfaces

The AK-ENU3M2-04 is the most interesting of the lot. In addition to supporting both SATA and NVMe SSDs, it also sports Type-A and Type-C male connectors. There is no cable to carry around / misplace, and the dual interface ensures that it is compatible with a wide range of systems. In addition, the tool-less design ensures that swapping SSDs is quick and painless. Overall, the AK-ENU3M2-04 ticks all the boxes for becoming part of the arsenal of computer support personnel.

The table below presents a comparative view of the specifications of the different storage bridges presented in this review.

S.M.A.R.T Passthrough - CrystalDiskInfo
Akasa AK-ENU3M2-04 (NVMe)Akasa AK-ENU3M2-04 (SATA)Akasa AK-ENU3M2-03Akasa AK-ENU3M2-02	Akasa AK-ENU3M2-04 (SATA)Akasa AK-ENU3M2-03Akasa AK-ENU3M2-02Akasa AK-ENU3M2-04 (NVMe)

Prior to looking at the benchmark numbers, power consumption, and thermal solution effectiveness of the different storage enclosures, a description of the testbed setup and evaluation methodology is provided.

Testbed Setup and Evaluation Methodology

Direct-attached storage devices (including storage enclosures) are evaluated using the Quartz Canyon NUC (essentially, the Xeon / ECC version of the Ghost Canyon NUC) configured with 2x 16GB DDR4-2667 ECC SODIMMs and a PCIe 3.0 x4 NVMe SSD - the IM2P33E8 1TB from ADATA.

The most attractive aspect of the Quartz Canyon NUC is the presence of two PCIe slots (electrically, x16 and x4) for add-in cards. In the absence of a discrete GPU - for which there is no need in a DAS testbed - both slots are available. In fact, we also added a spare SanDisk Extreme PRO M.2 NVMe SSD to the CPU direct-attached M.2 22110 slot in the baseboard in order to avoid DMI bottlenecks when evaluating Thunderbolt 3 devices. This still allows for two add-in cards operating at x8 (x16 electrical) and x4 (x4 electrical). Since the Quartz Canyon NUC doesn't have a native USB 3.2 Gen 2x2 port, Silverstone's SST-ECU06 add-in card was installed in the x4 slot. All non-Thunderbolt devices are tested using the Type-C port enabled by the SST-ECU06.

The specifications of the testbed are summarized in the table below:

The testbed hardware is only one segment of the evaluation. Over the last few years, the typical direct-attached storage workloads for memory cards have also evolved. High bit-rate 4K videos at 60fps have become quite common, and 8K videos are starting to make an appearance. Game install sizes have also grown steadily even in portable game consoles, thanks to high resolution textures and artwork. Keeping these in mind, our evaluation scheme for portable SSDs and UFDs involves multiple workloads which are described in detail in the corresponding sections.

• Synthetic workloads using CrystalDiskMark and ATTO
• Real-world access traces using PCMark 10's storage benchmark
• Custom robocopy workloads reflective of typical DAS usage
• Sequential write stress test

A comprehensive overview of the performance of the different Akasa enclosures is provided in the following sections. Prior to providing concluding remarks, we have some observations on the power efficiency aspect also.

Synthetic Benchmarks - ATTO and CrystalDiskMark

Benchmarks such as ATTO and CrystalDiskMark help provide a quick look at the performance of the direct-attached storage device. The results translate to the instantaneous performance numbers that consumers can expect for specific workloads, but do not account for changes in behavior when the unit is subject to long-term conditioning and/or thermal throttling. Yet another use of these synthetic benchmarks is the ability to gather information regarding support for specific storage device features that affect performance.

Both SATA storage bridges are able to sustain the maximum possible transfer rates from SATA SSDs - in this case, the WD Red SA500 is able to provide around 510 MBps writes and 535 MBps reads for the ATTO workloads. The VL716-enabled AK-ENU3M2-02 is able to provide more consistent write performance compared to the AK-ENU3M2-04 using the Realtek RTL9210B-CG.

CrystalDiskMark Benchmarks - NVMe
TOP: Akasa AK-ENU3M2-03Akasa AK-ENU3M2-04 (NVMe)	BOTTOM: Akasa AK-ENU3M2-04 (NVMe)Akasa AK-ENU3M2-04 (NVMe)Akasa AK-ENU3M2-03

Both NVMe bridges behave similarly for sequential accesses. However, the ASMedia solution exhibits much better performance for high queue-depth 4K random accesses compared to the Realtek solution.

AnandTech DAS Suite - Benchmarking for Performance Consistency

Our testing methodology for storage bridges takes into consideration the usual use-case for such devices. The most common usage scenario is transfer of large amounts of photos and videos to and from the unit. Other usage scenarios include the use of the unit as a download or install location for games and importing files directly from it into a multimedia editing program such as Adobe Photoshop. Some users may even opt to boot an OS off an external storage device.

The AnandTech DAS Suite tackles the first use-case. The evaluation involves processing five different workloads:

• AV: Multimedia content with audio and video files totalling 24.03 GB over 1263 files in 109 sub-folders
• Home: Photos and document files totalling 18.86 GB over 7627 files in 382 sub-folders
• BR: Blu-ray folder structure totalling 23.09 GB over 111 files in 10 sub-folders
• ISOs: OS installation files (ISOs) totalling 28.61 GB over 4 files in one folder
• Disk-to-Disk: Addition of 223.32 GB spread over 171 files in 29 sub-folders to the above four workloads (total of 317.91 GB over 9176 files in 535 sub-folders)

Except for the 'Disk-to-Disk' workload, each data set is first placed in a 29GB RAM drive, and a robocopy command is issue to transfer it to the external storage unit (formatted in exFAT for flash-based units, and NTFS for HDD-based units).

robocopy /NP /MIR /NFL /J /NDL /MT:32 $SRC_PATH $DEST_PATH

Upon completion of the transfer (write test), the contents from the unit are read back into the RAM drive (read test) after a 10 second idling interval. This process is repeated three times for each workload. Read and write speeds, as well as the time taken to complete each pass are recorded. Whenever possible, the temperature of the external storage device is recorded during the idling intervals. Bandwidth for each data set is computed as the average of all three passes.

The 'Disk-to-Disk' workload involves a similar process, but with one iteration only. The data is copied to the external unit from the CPU-attached NVMe drive, and then copied back to the internal drive. It does include more amount of continuous data transfer in a single direction, as data that doesn't fit in the RAM drive is also part of the workload set.

AnandTech DAS Suite - Performance Consistency
TOP: Akasa AK-ENU3M2-03Akasa AK-ENU3M2-04 (NVMe)	BOTTOM: Akasa AK-ENU3M2-04 (NVMe)Akasa AK-ENU3M2-04 (NVMe)Akasa AK-ENU3M2-03

A similar scenario plays out for the NVMe bridges. Temperatures top out at 66C for the ASMedia bridge solution, and 80C for the Realtek one. The throttling is evident in the disk-to-disk transfer set, where the Realtek solution drops down to around 800 MBps for the majority of the write transfer duration, while the ASMedia solution sustains 1000 MBps+ for a much longer duration.

PCMark 10 Storage Bench - Real-World Access Traces

There are a number of storage benchmarks that can subject a device to artificial access traces by varying the mix of reads and writes, the access block sizes, and the queue depth / number of outstanding data requests. We saw results from two popular ones - ATTO, and CrystalDiskMark - in a previous section. More serious benchmarks, however, actually replicate access traces from real-world workloads to determine the suitability of a particular device for a particular workload. Real-world access traces may be used for simulating the behavior of computing activities that are limited by storage performance. Examples include booting an operating system or loading a particular game from the disk.

PCMark 10's storage bench (introduced in v2.1.2153) includes four storage benchmarks that use relevant real-world traces from popular applications and common tasks to fully test the performance of the latest modern drives:

• The Full System Drive Benchmark uses a wide-ranging set of real-world traces from popular applications and common tasks to fully test the performance of the fastest modern drives. It involves a total of 204 GB of write traffic.
• The Quick System Drive Benchmark is a shorter test with a smaller set of less demanding real-world traces. It subjects the device to 23 GB of writes.
• The Data Drive Benchmark is designed to test drives that are used for storing files rather than applications. These typically include NAS drives, USB sticks, memory cards, and other external storage devices. The device is subjected to 15 GB of writes.
• The Drive Performance Consistency Test is a long-running and extremely demanding test with a heavy, continuous load for expert users. In-depth reporting shows how the performance of the drive varies under different conditions. This writes more than 23 TB of data to the drive.

Despite the data drive benchmark appearing most suitable for testing direct-attached storage, we opt to run the full system drive benchmark as part of our evaluation flow. Portable flash drives are also used as boot drives and storage for Steam games. These types of use-cases are addressed only in the full system drive benchmark.

The Full System Drive Benchmark comprises of 23 different traces. For the purpose of presenting results, we classify them under five different categories:

• Boot: Replay of storage access trace recorded while booting Windows 10
• Creative: Replay of storage access traces recorded during the start up and usage of Adobe applications such as Acrobat, After Effects, Illustrator, Premiere Pro, Lightroom, and Photoshop.
• Office: Replay of storage access traces recorded during the usage of Microsoft Office applications such as Excel and Powerpoint.
• Gaming: Replay of storage access traces recorded during the start up of games such as Battlefield V, Call of Duty Black Ops 4, and Overwatch.
• File Transfers: Replay of storage access traces (Write-Only, Read-Write, and Read-Only) recorded during the transfer of data such as ISOs and photographs.

PCMark 10 also generates an overall score, bandwidth, and average latency number for quick comparison of different drives. The sub-sections in the rest of the page reference the access traces specified in the PCMark 10 Technical Guide.

Booting Windows 10

The read-write bandwidth recorded for each drive in the boo access trace is presented below.

Full System Drive Benchmark Bandwidth (MBps)Full System Drive Benchmark Latency (us)Full System Drive Benchmark ScoreExpand All

The SK hynix Gold P31 in the pure NVMe bridge solution scores 1214 compared to the 1122 of the multi-protocol solution.

Overall, we find that the multi-protocol Realtek RTL9210B-CG solution should not be preferred over pure bridge solutions when performance is important.

Miscellaneous Aspects and Concluding Remarks

The performance of the storage bridges in various real-world access traces as well as synthetic workloads was brought out in the preceding sections. We also looked at the performance consistency for these cases. Power users may also be interested in performance consistency under worst-case conditions, as well as overall power consumption. The latter is also important when used with battery powered devices such as notebooks and smartphones. Pricing is also an important aspect. We analyze each of these in detail below.

Worst-Case Performance Consistency

Flash-based storage devices tend to slow down in unpredictable ways when subject to a large number of small-sized random writes. Many benchmarks use that scheme to pre-condition devices prior to the actual testing in order to get a worst-case representative number. Fortunately, such workloads are uncommon for direct-attached storage devices, where workloads are largely sequential in nature. Use of SLC caching as well as firmware caps to prevent overheating may cause drop in write speeds when a flash-based DAS device is subject to sustained sequential writes.

Our Sequential Writes Performance Consistency Test configures the device as a raw physical disk (after deleting configured volumes). A fio workload is set up to write sequential data to the raw drive with a block size of 128K and iodepth of 32 to cover 90% of the drive capacity. The internal temperature is recorded at either end of the workload, while the instantaneous write data rate and cumulative total write data amount are recorded at 1-second intervals.

CrystalDiskMark Workloads - Power Consumption
TOP: Akasa AK-ENU3M2-03Akasa AK-ENU3M2-04 (NVMe)	BOTTOM: Akasa AK-ENU3M2-04 (NVMe)Akasa AK-ENU3M2-04 (NVMe)Akasa AK-ENU3M2-03

The ASMedia ASM2362 NVMe bridge solution configuration is significantly more power hungry compared to the multi-protocol Realtek RTL9210B-CG solution. The pure bridge solution consumes around 2.3W during active traffic and 1.5W at idle. In contrast, the Realtek solution consumes around 2W during active traffic and 1.2W / 0.4W at idle.

Market Availability and Pricing

Akasa distributes its SSD enclosures in multiple market regions. Unfortunately, they are not directly available in the North American market, with the focus in the US being more on their fanless PC cases.

In the UK, the pure SATA bridge (AK-ENU3M2-02) can purchase for GBP 25, and is also available in the US (shipped from UK) for $43. There are a large number of pure SATA bridge solutions available in the market - even ones using the same VIA Labs VL716 bridge. Depending on the market region, other similar options may be cheaper - such as this $16 one for US consumers.

The pure NVMe bridge (AK-ENU3M2-03) is available for GBP 60 or USD 50. The product doesn't seem to be as widely carried as the other two solutions. In any case, M.2 NVMe – USB-C bridge solutions are a dime a dozen nowadays. We have reviewed very effective and efficient solutions from MyDigitalSSD as well as Plugable (USD 50) previously. Cheaper options are available for this particular use-case.

The multi-protocol solution (AK-ENU3M2-04) is available for GBP 40. This is a unique product, and the only alternative we could find in the US market is the FIDECO M.2 NVMe & SATA SSD Enclosure Adapter for USD 31. The FIDECO model's case and main board seems to be exactly the same as the AK-ENU3M2-04 (possibly using the same OEM), though the bundled accessories are probably different. Readers in the US interested in the AK-ENU3M2-04 after reading this review can probably opt for the FIDECO model.

Final Words

Akasa's USB 3.2 Gen 2 (10Gbps) M.2 SSD enclosures lineup is quite comprehensive in terms of addressing various market requirements. The SATA-only and NVMe-only bridges are quite similar to other products in the market, and do not offer any compelling differentiation aspects. On the other hand, the multi-protocol solution in the AK-ENU3M2-04 is quite unique.

After using the AK-ENU3M2-04 heavily over the last couple of months, its pros and cons are quite clear. If performance is the sole requirement, the Realtek solution is not going to fit the bill. Rather, it shines as a tool for computer support technicians and people involved in frequently maintaining / servicing multiple PCs. In addition to supporting both SATA and NVMe SSDs, it also comes with both Type-A and Type-C connectors integrated. There is no need to carry around cables or search for the right cable when dealing with PCs that do not have a Type-C port. Essentially, it can act as a very high performance thumb drive. On the flip side, the absence of a thermal solution means that certain SSDs could get quite hot when subject to heavy traffic inside the enclosure. We have been using the SK hynix P31 in it, and the SSD throttles a bit only after more than 100GB of continuous writes. If heavy continuous traffic is expected, users can always opt to add their own thin thermal pad - the enclosure is aluminum and can easily conduct heat away.

Overall, Akasa's M.2 SSD enclosures lineup is quite comprehensive, with different products catering to different requirements. It is a pity that the company distributes only fanless PC cases in the NA region. Given the unique multi-protocol product in the lineup, we hope the company can start distributing them worldwide.