Miscellaneous Aspects and Concluding Remarks

The performance of the 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 Write to 90% of Disk Capacity - Performance Consistency (SATA-Class)

Both the HP P600 and the ADATA SC680 show signs of a SLC cache. On the other hand, the X6 starts off at around 200 MBps and goes down to around 35 MBps after 240GB of continuous writes. At 195 MBps, the drive already starts off with low expectations, and there is not much to write home about.

Sequential Write to 90% of Disk Capacity - Performance Consistency (NVMe-Class)

The X8, on the other hand, performs admirably with the SLC cache - For around 256GB of continuous writes, the drive provides 825 MBps+ of bandwidth before slipping down to around 150 MBps for the direct-to-QLC writes. The reason for the X8's stellar performance for normal workloads lies in this SLC cache. Normal workloads rarely go beyond this huge cache, and that is enough to make the X8 lead the charts in almost all tests. The problem is when the SLC cache runs out - as is possible for creative professionals transferring huge work files. Crucial does mention read-intensive workloads as the main focus of the drive, and hence folks with those types of workloads may well prefer SSDs such as the SanDisk Extreme PRO v2.

Power Consumption

Bus-powered devices can configure themselves to operate within the power delivery constraints of the host port. While Thunderbolt 3 ports are guaranteed to supply up to 15W for client devices, USB 3.0 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 drives. Using the Plugable USBC-TKEY, the bus power consumption of the drives was tracked while processing the CrystalDiskMark workloads (separated by 30s intervals). The graphs below plot the instantaneous bus power consumption against time, while singling out the maximum and minimum power consumption numbers.

Drive Power Consumption - CrystalDiskMark Workloads (SATA-Class)

The X6 seems to have a power consumption profile similar to other drives in the set. The 1W+ idling number is a bit too high for our liking when attempting to use the drive with battery-powered devices, but the competition is not much better in any case.

Drive Power Consumption - CrystalDiskMark Workloads (NVMe-Class)

The X8 2TB version consumes less power than the 1TB version from last year. In addition, the peak power consumption is the lowest for the X8 2TB drive. Idle power consumption is not as good, with the OWC Envoy PRO EX USB-C being much more efficient on that front.


The price of flash-based storage devices tend to fluctuate quite a bit over time. However, the relative difference between different models usually doesn't change. The table below summarizes the product links and pricing for the various units discussed in the review.

SATA-Class External Flash Storage Devices - Pricing
Product Model Number Capacity (GB) Street Price (USD) Price per GB (USD/GB)
ADATA SC680 960GB ASC680-960GU32G2 960 $125 0.1302
Crucial Portable SSD X6 2TB CT2000X6SSD9 2000 $285 0.1425
HP P600 500GB 3XJ07AA#ABC 500 $80 0.16

The X6 is not very competitively priced, particularly given the pricing for the higher-performance 2TB drives belonging to the NVMe class. In fact, just an additional $15 gets the consumer to the WD My Passport 2TB NVMe external SSD.

NVMe-Class External Flash Storage Devices - Pricing
Product Model Number Capacity (GB) Street Price (USD) Price per GB (USD/GB)
Crucial Portable SSD X8 1TB CT1000X8SSD9 1000 $150 0.15
WD My Passport SSD (2020) 1TB WDBAGF0010BGY 1000 $150 0.15
Crucial Portable SSD X8 2TB CT2000X8SSD9 2000 $307 0.1535
SanDisk Extreme Portable SSD v2 1TB SDSSDE61-1T00 1000 $160 0.16
SanDisk Extreme PRO Portable SSD v2 2TB SDSSDE81-2T00 2000 $380 0.19
OWC Envoy Pro EX USB-C 2TB ENVPROC2N20 1920 $399 0.2078

The X8 also falls into the same category - the pricing is simply too high for a QLC drive. At $307, it is even priced higher than the 2TB My Passport NVMe SSD. Though we haven't reviewed the 2TB version of the My Passport SSD (2020), our experience with the 1TB version was quite satisfactory.

Final Words

After careful analysis of various aspects (including benchmark numbers, temperatures, power consumption, and pricing), it is clear that the Crucial Portable SSD X8 is an excellent choice for normal consumer workloads. The X6, unfortunately, is not as attractive given its pricing. In the X8, Crucial must be appreciated for delivering a SSD for those types of workloads that successfully manages to hide the shortcomings of QLC. Unfortunately, users have to shell out for the highest-capacity version to get the 256GB of SLC cache (The 1TB version has half the cache). The thermal profile of both drives is good enough to prevent them from getting too hot to touch. The X8 gets our recommendation for normal consumer workloads, but the Western Digital drives are a better choice for creative professionals and users with write-intensive workloads, and they currently cost less than the X8. The absence of any IP rating and hardware encryption are minor quibbles, but Crucial does offer drop-protection with both the X6 and the X8. In the end, the recommendation for the end-user will depend on the expected usage scenarios.

PCMark 10 Storage Bench - Real-World Access Traces
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  • Duncan Macdonald - Thursday, October 22, 2020 - link

    This is QLC flash - most QLC will not reach beyond 1000 cycles - some will only reach a few hundred - the rated TBW IS important. Also the write speed on QLC often degrades as the cycle count increases.
  • zepi - Thursday, October 22, 2020 - link

    I don't care slightest about write endurance - I have hard time envisioning a use case where this kind of drive is written to death. Even few hundred P/E cycles is a lot for a normal person. If you are not a "normal person" and your workload is heavy, then go and buy something else.

    However, what I'd be very afraid is the data retention. QLC - drive being unplugged for reasonably long periods of time etc.

    It is completely normal for people to take backups, transfer bunch of files etc. and expect them to be readable in half a year from writing after storing the drive in the glove compartment of their car or whatever crazy people do.

    Is the data readable after such period? No idea.
  • AMDSuperFan - Thursday, October 22, 2020 - link

    Ganesh - looking at the boxes in your picture they look pretty much banged up. Were these new or used drives that you tested here? I think you are an excellent writer.
  • Oxford Guy - Monday, October 26, 2020 - link

    "The emergence of 3D NAND with TLC and QLC has brought down the cost of such drives."

    You meant:

    The emergence of 3D NAND with TLC has brought down the cost of such drives. QLC, meanwhile, is about increasing margin for drive makers and decreasing quality for consumers."
  • Oxford Guy - Monday, October 26, 2020 - link

    "I don't care slightest about write endurance - I have hard time envisioning a use case where this kind of drive is written to death. Even few hundred P/E cycles is a lot for a normal person. If you are not a "normal person" and your workload is heavy, then go and buy something else. However, what I'd be very afraid is the data retention. QLC - drive being unplugged for reasonably long periods of time etc."

    Drive death in the consumer realm has always been mainly about firmware/controller bugs (or, possibly defective NAND), not the NAND wearing out through use. The most extreme examples I can think of are the Sandforce 2 controllers from OCZ that bricked drives when OCZ switched to 64-bit planar MLC (without telling anyone) and Intel's G2 drive that had a data corruption problem due to bad firmware.

    (The Sandforce problem was never solved by a plethora of firmware patches. OCZ pretended that it solved the issue by letting people return the drives but the people who spent the most money (on the highest capacity drives, the 240 GB ones) were not allowed to return them! I have three bricked 240 GB OCZ drives. Two of them are drives OCZ sent when the first ones bricked.)

    The differences between things like planar MLC and planar TLC have been about other problems. Planar TLC from Samsung didn't result in drive death (the red herring everyone talks about). Instead, it was voltage drift that caused the data to have to be constantly rewritten as a kludge "solution" to very poor performance. That much more frequent writing slows performance, makes one question the safety of storing the drive powered off for long periods, and can lead to the NAND wearing out I suppose.

    Drive death from worn-out NAND has been a red herring for the most part, while other serious drawbacks to increasing the number of voltage states (by adding layers) have been whitewashed. Well, it looks like QLC brings back the drive death from worn-out NAND problem back a bit while having all of the drawbacks of there being so many more voltage states (which increases the problem of drift drastically).

    The only things going for it is that it's 3D instead of planar and that capacities have increased which helps to mask the issue for most consumer workloads. Regardless, I consider QLC to be an unsatisfactory solution to a problem consumers didn't face: how to increase margin for the companies selling drives beyond what 3D TLC offers. That's the real driving force being QLC. It is not giving consumers a much better capacity deal for their money. The economy of scale factor, instead, works against consumer value by increasing the price of 3D TLC. Companies use that as an excuse to keep prices of QLC too high. Neat trick, for as long as they can make it last. By winding down TLC capacity, they can do it for as long as they like, so long as no one decides to fight the current and keep high volume TLC production going and reasonable pricing for it (in defiance of the scarcity dynamic).
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    I guess there is no need to compare 35$ product with the expensive one
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