Flash-based portable drives have become popular for fast storage from the perspective of both content creators and backups-seeking consumers. The advent of high-speed interfaces such as USB 3.2 Gen 2 (10 Gbps) and USB 3.2 Gen 2x2 (20 Gbps) along with Thunderbolt 3 (up to 40 Gbps) have enabled rapid improvements in performance of such portable SSDs over the last few years.

The higher-speed (20 Gbps+) variants had traditionally been restricted to premium devices. Additionally, USB 3.2 Gen 2x2 was turning out to be an odd standard, as USB4 opted to support only features of USB 3.2 Gen 2 from a backwards compatibility perspective. On both the host and device side, ASMedia was the only silicon vendor for more than a year. However, the introduction of more host platforms (such as Intel's latest 600 series chipset) with native support for USB 3.2 Gen 2x2 and the appearance of native 20 Gbps USB flash drive (UFD) controllers from Phison and Silicon Motion have enabled the 20 Gbps standard to gain more traction. Our preview of the Silicon Motion SM2320 showed scope for the appearance of cost-effective USB 3.2 Gen 2x2 portable SSDs with excellent value propositions.

The Kingston XS2000 series is the first portable SSD family to use Silicon Motion's SM2320 platform. Available in three capacities - 500GB, 1TB, and 2TB, the drives promise speeds of up to 2000 MBps. The company sent across samples of all three capacity points in the lineup to put through our rigorous direct-attached storage evaluation process. The review below presents the detailed evaluation report of drives, with emphasis on the aspects that were not covered in the UFD controller preview.

Introduction and Product Impressions

External bus-powered storage devices capable of 1GBps+ performance have become entry-level offerings in the market today, with 2GBps+ starting to become mainstream. Rapid advancements in flash technology (including the advent of 3D NAND and NVMe) as well as faster host interfaces (such as Thunderbolt 3 and USB 3.2 Gen 2+) have been key enablers. Broadly speaking, there are five distinct performance levels in this market:

• 2GBps+ drives with Thunderbolt 3, using NVMe SSDs
• 2GBps drives with USB 3.2 Gen 2x2, using NVMe SSDs or direct USB flash drive (UFD) controllers
• 1GBps drives with USB 3.2 Gen 2, using NVMe SSDs or direct UFD controllers
• 500MBps drives with USB 3.2 Gen 1 (or, Gen 2, in some cases), using SATA SSDs
• Sub-400MBps drives with USB 3.2 Gen 1, using UFD controllers

The Kingston XS2000 we are looking at today belongs to the second category in the above list, utilizing flash packaged directly behind the Silicon Motion SM2320 UFD controller.

The package includes the main unit, a rubber sleeve, and a 30 cm. Type-C to Type-C cable rated for 20Gbps operation.

The compact casing is a mix of metal and plastic, and the supplied rubber sleeve supports its IP55 rating for limited protection against dust ingress and splashing of liquids.

The availability of all three capacity points enables us to compare the XS2000 against almost all previously reviewed USB 3.2 Gen 2x2 drives. The list of portable SSDs evaluated as part of this review is provided below:

• Kingston XS2000 2TB
• Kingston XS2000 1TB
• Kingston XS2000 500GB
• Seagate FireCuda 1TB
• Silicon Motion SM2320XT 1TB Reference Design
• Silverstone MS12 DIY USB 3.2 Gen 2x2 SSD with SK hynix Gold P31 1TB NVMe SSD
• WD_BLACK P50 1TB

CrystalDiskInfo provides a quick overview of the capabilities of the internal storage device. Since the program handles each bridge chip differently, and the SM2320 inside the Kingston XS2000 is quite new, many of the entries are marked as vendor-specific, and some of the capabilities (such as the interface) are deciphered incorrectly. The temperature monitoring worked well, though - just like it did for the reference design.

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

Testbed Setup and Evaluation Methodology

Direct-attached storage devices (including portable SSDs) 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 Kingston XS2000 portable SSDs is provided in the following sections. Prior to providing concluding remarks, we have some observations on the power efficiency aspect of the drives also.

Synthetic Benchmarks - ATTO and CrystalDiskMark

Benchmarks such as ATTO and CrystalDiskMark help provide a quick look at the performance of direct-attached storage devices. 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.

Kingston claims read and write speeds of up to 2000 MBps for all capacities, and the read side numbers are backed up by the ATTO benchmarks provided below. ATTO benchmarking is restricted to a single configuration in terms of queue depth, and is only representative of a small sub-set of real-world workloads. It does allow the visualization of change in transfer rates as the I/O size changes, with optimal performance being reached around 4 MB for a queue depth of 4. For this queue depth, the writes saturate at around 1.75 GBps and this is well south of the 2000 MBps claimed on the product packaging.

CrystalDiskMark Benchmarks
TOP: Kingston XS2000 2TBKingston XS2000 1TBKingston XS2000 500GBSilverstone MS12WD_BLACK P50 1TBSilicon Motion SM2320XT 1TBSeagate FireCuda 1TB	BOTTOM: Kingston XS2000 1TBKingston XS2000 500GBSilverstone MS12WD_BLACK P50 1TBSilicon Motion SM2320XT 1TBSeagate FireCuda 1TBKingston XS2000 2TB

The bandwidth numbers for specific read workloads exceed Kingston's claims (reaching as high as 2089 MBps for the 2TB version), but writes seem to be capped slightly north of 1800 MBps even for sequential access traces. The reads manage to match bridge-based solutions (including the DIY one), while writes fall behind. In the random access traces, the DRAM-less nature of the controller results in performance loss for high queue depth operations. At low queue depths, the write performance can match the bridge-based solutions with DRAM-equipped NVMe SSDs, while the read numbers fall slightly behind.

AnandTech DAS Suite - Benchmarking for Performance Consistency

Our testing methodology for portable SSDs 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: Kingston XS2000 2TBKingston XS2000 1TBKingston XS2000 500GBSilverstone MS12WD_BLACK P50 1TBSilicon Motion SM2320XT 1TBSeagate FireCuda 1TB	BOTTOM: Kingston XS2000 1TBKingston XS2000 500GBSilverstone MS12WD_BLACK P50 1TBSilicon Motion SM2320XT 1TBSeagate FireCuda 1TBKingston XS2000 2TB

The first three sets of writes and reads correspond to the AV suite. A small gap (for the transfer of the video suite from the internal SSD to the RAM drive) is followed by three sets for the Home suite. Another small RAM-drive transfer gap is followed by three sets for the Blu-ray folder. This is followed up with the large-sized ISO files set. Finally, we have the single disk-to-disk transfer set. The 2TB version exhibits perfect consistency between different passes, while the 500GB version starts showing consistency problems in the second suite itself.

The thermal performance of the XS2000 enclosure is excellent, with the temperatures staying well south of 75C throughout the workload for all SKUs. Of particular interest is the comparison of the SM2320 reference design (1TB) against the XS2000 SKU of the same capacity. While the reference design without any thermal solution landed up around 86C at the end of the test (completing it in around 2040s), the XS2000 seems to trigger a bit of thermal throttling in the disk-to-disk workload segment. While the temperature remained in check, the write workload took around 3 extra minutes to complete. This is also reflected in the disk-to-disk write bandwidth graph of the previous subsection, with the reference design landing at around 325MBps compared to the XS2000 1TB's 275MBps.

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. Many of us use portable flash drives 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

Overall, we see the SX2000 2TB SKU perform admirably, landing in the top half of the pack. However, the 500GB SKU suffers heavily - the bandwidth is half, and the latency double of what consumers have been expecting from 2GBps-class portable SSDs.

Miscellaneous Aspects and Concluding Remarks

The performance of the three Kingston XS2000 SKUs 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 drive 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: Kingston XS2000 2TBKingston XS2000 1TBKingston XS2000 500GBSilverstone MS12WD_BLACK P50 1TBSilicon Motion SM2320XT 1TBSeagate FireCuda 1TB	BOTTOM: Kingston XS2000 1TBKingston XS2000 500GBSilverstone MS12WD_BLACK P50 1TBSilicon Motion SM2320XT 1TBSeagate FireCuda 1TBKingston XS2000 2TB

The 2TB version with additional flash packages consumes slightly more power during active periods than the 1TB version, which in turn consumes more than the 500GB version. Peak power also follows a similar trend - 3.26W for the 500GB, 3.95W for the 1TB, and 4.74W for the 2TB. These are still much lower than the 8W+ for the FireCuda Gaming SSD and the WD_BLACK P50 and the 5.5W+ for the DIY SSD. The XS2000 also enters a deep sleep state with pretty much no power consumption from the host port after around 20 minutes of absence of any host traffic.

Final Words

The Kingston XS2000 series manages to bring a high-performance native UFD controller-based portable SSD in a compact and attractive package. The most attractive aspect, however, is the pricing structure. The 500GB SKU is priced at $85, the 1TB version is just $135, and the 2TB SKU is at $240. One of the key advantages of a UFD controller-based solution is the reduced BOM cost, and this is brought out in the pricing structure. For comparison, a DIY 1TB solution ends up at around $180, while the WD_BLACK P50 is priced at $190. It can be observed that the single-chip solution ends up around $50 cheaper. In fact, the XS2000 is priced lower than some of the bridge-based USB 3.2 Gen 2 (10 Gbps / 1GBps-class) solutions in the market too. There is no doubt that the Kingston XS2000's value proposition is excellent.

In terms of performance and consistency, the XS2000 SKUs behave similar to a DRAM-less PCIe 3.0 x4 NVMe SSD behind a USB 3.2 Gen 2x2 bridge. The 2TB SKU is perfect for most DAS workloads. Unless the end-user is expecting to work with more than 390 GB of data in one go, the effective SLC cache enables the drive to deliver performance rivaling that of high-end SSDs such as the SanDisk Extreme PRO v2. Obviously, under stressful scenarios with large number of random writes and / or after the running out of the SLC cache, the performance of the drive suffers much more than bridge-based solutions with high-end DRAM-equipped NVMe SSDs. That, however, is part of the price - performance trade-off. Another advantage is power efficiency. The single-chip solution with fewer board components sips power compared to the guzzling of the bridge-based solutions.

The effective SLC cache size and thermal design are major contributors to the user experience with portable SSDs. The limited SLC cache in the 500GB model (20GB - around 4% of the drive capacity) puts a spanner in the works, delivering a SATA SSD-like performance even under moderate stress. Our experience with the 1TB SKU was very similar to the one we had with the SM2320 reference design, with the thermal design managing to keep the SSD cool without extensive throttling. With a SLC cache of around 10% of the drive capacity, the 1TB SKU should tick most boxes for the average consumer. The 2TB version of the Kingston XS2000 is the real winner - It fits the requirements of a vast majority of the consumers without breaking the bank.

With the XS2000 portable SSD family, Kingston and Silicon Motion have managed to bring the benefits of USB 3.2 Gen 2x2 to consumers at mainstream price points. As host support for the standard expands, that is excellent news for the ecosystem.