Power Consumption and Concluding Remarks

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 2.5W (500mA @ 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

The Gen 2x2 Extreme PRO v2 has a peak power consumption of around 7.23W, and idles at around 3W. It does go to sleep after around 20 minutes, dropping down to 0.91W. The X6 on the other hand has a peak power consumption of 2.95W. The idling power is around 0.75W. The drive didn't go to a lower power state below the 0.75W mode - in fact, after some idling time, it appears that some sort of garbage collection / moving of data from SLC to QLC takes place that causes significant power spikes.

Final Words

The preceding sections took a detailed look at two 4TB external SSDs - the SanDisk Extreme PRO Portable SSD v2 focusing on no-holds barred performance, and the Crucial X6 Portable SSD targeting the mainstream market with affordability as its primary focus.

Western Digital/SanDisk has taken the highest-performing USB bridge chip in the market, and coupled that with their highest performance SSD sporting full compatibility with that bridge chip. One could argue that a Thunderbolt 3 SSD would exhibit better performance, but the counter for that involves two different aspects - getting a Thunderbolt 3 SSD to work with USB hosts is necessary for wider compatibility, particularly for the Extreme PRO v2's target market. This involves integrating a USB bridge chip as well as a separate Thunderbolt 3 device controller on the board, increasing BOM cost and complexity. Additionally, Windows appears to treat Thunderbolt 3 SSDs as internal PCIe SSDs - when coupled with the default write caching disabled state, the write performance of Thunderbolt 3 SSDs becomes abysmal compared to even USB 3.2 Gen 2 (10 Gbps) SSDs. As seen in the benchmark numbers, the Extreme PRO v2 handily surpasses all Thunderbolt 3 SSDs in write-intensive workloads.

Crucial has gone in for aggressive optimizations in terms of platform cost. The product comes with a single Type-C to Type-C cable, and the Type-C to Type-A adapter is a separate purchase. Almost all modern PCs come with Type-C ports, so this might not be a concern for most consumers, but it does allow Crucial to push the pricing down further for the base SKU. The company has also not pursued any IP-rating for the device (the Extreme PRO v2 is IP55-rated). And unlike the Extreme PRO v2, the X6 doesn't feature hardware encryption. While the previous X6 had flash chips, a SATA SSD controller, and a bridge chip, the 4TB SKU comes with the flash chips and a native UFD (USB flash drive) controller. Coupling that with the use of QLC NAND (compared to Western Digital's 3D TLC in the Extreme PRO v2) means that the X6 offers the same storage capacity at a price point that is around half that of the SanDisk Extreme PRO v2.

Both SSDs support TRIM and S.M.A.R.T pass through, which are essential for keeping the drive healthy and monitoring it. Content creators and power users will definitely appreciate the SanDisk Extreme PRO v2 for its combination of features and performance. That great performance does come at a price, however, and after launching at $750 back in January, the drive now retails for $900. Despite the premium, it is likely that there is a significant market for the drive given how little competition there is within its performance class. The only downside for Western Digital is that USB 3.2 Gen 2x2 (20 Gbps) is yet to gain widespread traction, but that seems to be slowly changing.


Casual users will find the Crucial X6 at $480 fitting their requirements quite well. Though based on QLC NAND, with almost 800GB of SLC cache, most users are unlikely to run into the abysmal 75 MBps and 50 MBps writes. The drive also seems to be aggressive about moving data from the SLC buffer to its final place within the QLC NAND, and hence it is bound to regain performance quite quickly. At lower capacities, QLC could be quite problematic even for mainstream use-cases, but at 4TB – and with almost 20% of the capacity configured as SLC – it shouldn't matter. If better performance is desired, one has to be ready to fork out more – Western Digital has a host of 4TB 3D TLC options ranging from $680 to $900.

Worst-Case Performance Consistency


View All Comments

  • eastcoast_pete - Wednesday, August 18, 2021 - link

    I find it unfortunate that neither manufacturer found a way to integrate at least a few inches/centimeters of cable with USB connector into the case. You could still have another port/connector for an actual cable, but having let's say 6 inches/ 15 cm of cable with plug always attached (cable stored in a groove around the case) avoids the situation when one really needs to back up or save some larger files in a pinch, but then the cable is MIA. That's one of the reasons why USB sticks are so handy (can't lose the connector, you either have the stick or you don't), but they don't reach the speed or capacity of these external SSDs. Reply
  • damianrobertjones - Wednesday, August 18, 2021 - link

    cables can snap off, break etc. Then again so can the connector. I'd rather buy x3 cables for a sensible price. one at work, one at home, one to travel. Reply
  • meacupla - Wednesday, August 18, 2021 - link

    ew, no, that's disgusting
    Integrated cable is easily the worst and cheapest way to design things. Cables are, easily, the most likely connection to fail, and you want to integrate that?

    The only thing worse is a micro USB3.0 connector

    USB 3.0 A or USB-C, male, with a dust cover is an acceptable alternative, but female USB-C connector is so convenient, why would you use anything else?
  • flyingpants265 - Wednesday, August 18, 2021 - link

    Integrate a removable cable. Problem solved. Reply
  • watersb - Wednesday, August 18, 2021 - link

    Better: integrate a microUSB 3.0 cable. Now you have two problems. Reply
  • whatthe123 - Wednesday, August 18, 2021 - link

    or you could just have a slot for the removable cable instead of adding another point of failure Reply
  • aparangement - Wednesday, August 18, 2021 - link

    I think thermal capacity is the major bottleneck. You either live with slow USB stick which is cool and light, or PSSD with seperate cable, since the increased weight makes the connector more vulnerable. Reply
  • Sivar - Wednesday, August 18, 2021 - link

    It seems both products are priced reasonably. It's rare that I really need a portable drive to be Tesla quick, so I think the Crucial drive is a great deal for me, perhaps for most people. Reply
  • evanh - Wednesday, August 18, 2021 - link

    The X6 fails in the sequential bulk copy dept. That's a primary use case for external storage devices. Reply
  • ganeshts - Friday, August 20, 2021 - link

    It performs great for up to 800GB of continuous traffic. Can't imagine a casual user transferring that much amount of data in one go. As I mentioned in the concluding section, power users with such demanding requirements have to be ready to fork out a premium for the full-capacity consistency that the SanDisk Extreme PRO v2 provides. Reply

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