WD_BLACK P40 Game Drive USB 3.2 Gen 2×2 Portable SSD Review: Balanced Storage

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.

Western Digital claims read and write speeds of 2000 MBps, but these are not backed up by any of our usual synthetic benchmarks. As we shall see further down in this review, the P40 can sustain the advertised numbers only over a very small data size. One can run ATTO with a 256MB file size and CrystalDiskMark with a 1GB span and back up WD’s numbers, but those are not the sizes we use for evaluation.

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. For a 32GB file size, optimal write performance is reached for an I/O size of 128KB. Reads are ot affected much, reaching very close to advertised numbers at 512KB and sustaining it beyond that for a queue depth of 4. It is a matter of concern that none of the other 20 Gbps-class PSSDs have a problem with the ATTO file size used in our evaluation.

ATTO Benchmarks
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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 random accesses. Internally, CrystalDiskMark uses the Microsoft DiskSpd storage testing tool. The ‘Seq128K Q32T1’ sequential traces use 128K block size with a queue depth of 32 from a single thread, while the ‘4K Q32T16’ one does random 4K accesses with the same queue configuration, but from multiple threads. The ‘Seq1M’ traces use a 1MiB block size. The plain ‘Rnd4K’ one uses only a single queue and single thread . Comparing the ‘4K Q32T16’ and ‘4K Q1T1’ 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.

CrystalDiskMark Benchmarks
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The P40 can only average around 1250 MBps writes over a 32GB span. Every other PSSD in its class can sustain 1800 MBps+ for similar sequential accesses. The reads and high-queue depth random accesses are a bit of a saving grace for the P40 when compared to other PSSDs. Low queue-depth performance suffers due to the lack of on-board DRAM.

Our testing methodology for storage bridges / direct-attached storage units 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.

The P40 is in the top three in all of the read workloads. The writes are a different case altogether – the performance is sometimes even worse than 1GBps-class PSSDs such as the Samsung T7 Touch. The write penalty is particularly high for small-sized files. Power users may want to dig deeper to understand the limits of each device. To address this concern, we also instrumented our evaluation scheme for determining performance consistency.

Performance Consistency

Aspects influencing the performance consistency include SLC caching and thermal throttling / firmware caps on access rates to avoid overheating. This is important for power users, as the last thing that they want to see when copying over 100s of GB of data is the transfer rate going down to USB 2.0 speeds.

In addition to tracking the instantaneous read and write speeds of the DAS when processing the AnandTech DAS Suite, the temperature of the drive was also recorded. In earlier reviews, we used to track the temperature all through. However, we have observed that SMART read-outs for the temperature in NVMe SSDs using USB 3.2 Gen 2 bridge chips end up negatively affecting the actual transfer rates. To avoid this problem, we have restricted ourselves to recording the temperature only during the idling intervals. The graphs below present the recorded data.

AnandTech DAS Suite – Performance Consistency
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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. It can be seen that the P40 can indeed go as high as 1800 MBps for the writes, but only for a very short duration. The good news seems to be that it appears to regain the SLC cache relatively quickly. Sustained writes are a problem for the drive, unfortunately. The above graphs show the reason for the PSSD’s abysmal showing in the graphs in the previous sub-section. On the thermal front, the temperature is lower than all other 2GBps-class PSSDs except the Seagate Firecuda (which has a completely different performance profile allowing it to cool down rapidly towards the end of the test).

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.

The read-heavy nature of the workload allows the P40 to shine here. As we saw in the earlier sections, reads are the strong suite for the P40.

Creative Workloads

The read-write bandwidth recorded for each drive in the sacr, saft, sill, spre, slig, sps, aft, exc, ill, ind, psh, and psl access traces are presented below.

Creative workloads are either read-heavy (startup cases) or deal with small writes. Fortunately for the WD_BLACK P40, the writes fit within the SLC cache of the drive. It also appears that the drive has enough time to recover the SLC cache, allowing the P40 to be in the top 3 performers across all the workloads in this segment.

Office Workloads

The read-write bandwidth recorded for each drive in the exc and pow access traces are presented below.

Office workloads appear to be a bit of a challenge for the firmware optimizations in the WD_BLACK series. In fact, we see the gaming-focused SSDs from both WD and Seagate not performing well in both sub-tests.

Gaming Workloads

The read-write bandwidth recorded for each drive in the bf, cod, and ow access traces are presented below.

Moving on to the workloads relevant to the P40’s target market, we find the tag of a mid-range product working well for the drive. It lands right in the middle of the pack in all three game-loading scenarios.

Files Transfer Workloads

The read-write bandwidth recorded for each drive in the cp1, cp2, cp3, cps1, cps2, and cps3 access traces are presented below.

Read-only and mixed workloads see the P40 performing fairly well for a mid-range product, but the write-heavy workloads are it slip down in the rankings.

Overall Scores

PCMark 10 reports an overall score based on the observed bandwidth and access times for the full workload set. The score, bandwidth, and average access latency for each of the drives are presented below.

The P40 lives up to its mid-range moniker well, performing very decently across the board to land in the top three in the overall results.

The performance of the storage bridges / drives 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.

Sequential Writes to 90% Capacity – Performance Consistency
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The WD_BLACK P40 can sustain its advertised numbers for around 3 seconds before running out of SLC cache (this is with an empty drive). This translates to around 5.5 GB of SLC cache. Any data span beyond this results in a performance drop (down to the 600 MBps range). Only the Kingston XS2000 has a worse performance profile in this test, but that has the excuse of sporting a native UFD controller.

Power Consumption

Bus-powered devices can configure themselves to operate within the power delivery constraints of the host port. While Thunderbolt ports are guaranteed to supply up to 15W for client devices, USB 2.0 ports are guaranteed to deliver only 4.5W (900mA @ 5V). In this context, it is interesting to have a fine-grained look at the power consumption profile of the various external drives. Using the Plugable USBC-TKEY, the bus power consumption of the drives was tracked while processing the CrystalDiskMark workloads (separated by 5s intervals). The graphs below plot the instantaneous bus power consumption against time, while singling out the maximum and minimum power consumption numbers.

CrystalDiskMark Workloads – Power Consumption
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The power consumption profile of the P40 is much better than the P50 despite the addition of the RGB lighting (which is on by default). A peak of 5.73W and a low-power idling state of 0.92W are good to see in a 20Gbps PSSD. The drive also enters the low-power state much quicker (5 minutes after last activity) compared to the P50 (around 20 minutes after last activity). A complete turn-off mode is implemented in the Seagate Firecuda (goes to around 0.2W) – that would be nice to see here. The Kingston XS2000 has a much lower power consumption number, but that is only expected given its single-chip UFD controller solution.

Pricing and Competitive Positioning

USB 3.2 Gen 2×2 PSSDs generally carry a pricing premium over the vanilla PSSDs. This has come down a bit after the introduction of native UFD controllers supporting the high-speed interface. With the WD_BLACK P40, Western Digital has brought down the pricing to normal USB 3.2 Gen 2 PSSD levels of last year.

The 1TB version evaluated above comes in at $130. At a similar capacity point, the P50 lands at $200. The XS2000 is obviously cheaper at $110, while the FireCuda is priced at $190. In terms of pricing, the P40 is hard to beat. For read-heavy workloads, it is a no-brainer. For writes, it performs better than the XS2000 over the whole drive span. However, for typical game sizes between 10GB and 100GB, the transfer time to the XS2000 is bound to be shorter given its 98GB SLC cache. The XS2000 also doesn’t have RGB lighting – so the P40 has a slight edge here in the gaming market.

Final Words

The WD_BLACK P40 Game Drive is an interesting budget addition to the gaming-targeted lineup. The lack of performance consistency in writing out huge amounts of data (common when transferring large Steam libraries between systems, for example) is a deal-breaker for performance enthusiasts. However, the drive is able to make use of the high-speed interface well when reading out data. So, the drive could still be beneficial to a subset of the gaming crowd – folks who rarely write out whole games to the drive, but play thenm directly off the PSSD. A segment of gamers may also appreciate the infusion of RGB lighting. The drive is also a solid mid-range performer for traditional use-cases as shown in the PCMark storage workloads.

The most attractive feature of the drive is the pricing. Our recommendation for overall performance and feature set for gamers looking to purchase a USB 3.2 Gen 2×2 drive continues to be the WD_BLACK P50. The SanDisk Extreme PRO v2 (targeting a different market segment) will probably be a better bet if a fancy industrial design, RGB, and other gamers-desired features are not essential. Western Digital offers PSSDs tuned for different price points in a wide range of markets. In that context, the P40 fills an important hole in the company’s portfolio even though it might not take the performance crown.