Crucial X6 4TB Portable SSD review: Decent speed, good price to performance

Posted:
in General Discussion edited July 4
The Crucial X6 4TB Portable SSD is a cost-effective pocket-sized external SSD ideal for on-the-go storage for your Mac, with decent access speeds.

Crucial's X6 4TB is small and simply designed.
Crucial's X6 4TB is small and simply designed.


If you're carting around a MacBook Air and need some extra storage capacity, there are many options on the market that you could pick up. Main points of differentiation are speed, size, and sturdiness, and it's generally quite hard to find an external drive that can cover all three well.

The Crucial X6 is a very small external SSD that connects over USB 3.1 type C. The size allows you to easily stow it away in a bag and pull it out whenever it's required.

We've been using the 4TB variant, which Crucial rolled out in March 2021. At the time, it joined the roster alongside a 1TB and 2TB version, and the storage producer in parallel also increased the connection speed to match the larger capacity.

Key specs

  • Options for up to 4TB available.
  • USB-C 3.1 Gen 2 connectivity.
  • Compatible with earlier USB versions.
  • Sequential read speeds of up to 800MB/s claimed.
  • 2.7 inches by 2.5 inches by 0.43 inches.
  • 3-year warranty.

Size and design

The unassuming drive is uninspiring in design, but not everything needs to be forged by Jony Ive. It is a small square plastic enclosure, with a USB-C port on one side and the Crucial logo printed on the top panel.

It's not going to win awards with its appearance, but it's certainly adequate and what some would consider a fairly typical appearance for such an item.

The compact size of the Crucial X6 makes it highly portable.
The compact size of the Crucial X6 makes it highly portable.


The drive measures 69mm by 64mm (2.7 inches by 2.5 inches) and is just 11mm (0.43 inches) thick. It's also lightweight at about 40 grams (1.4 ounces).

Crucial has included a short USB Type-C to USB Type-C cable in the box, but if you carry one around anyway, it's one less thing to put into the bag. With a suitable cable or adapter, it can also connect to USB-A 3.0 or USB 2.0 ports at a corresponding drop in speed.

The Crucial X6 is also very thin (Sharpie for scale)
The Crucial X6 is also very thin (Sharpie for scale)


The company notes that the drive has shock and vibration resistance, and it is rated for drops of up to 6.5 feet.

It won't weigh down your bag, and it will easily be able to withstand being jostled around in the bag, too.

Capacity and performance

Before releasing the 4TB version, Crucial's X6 lineup was marketed as having sequential read speeds of up to 540MB/s. The 4TB model alone is rated at up to 800MB/s, all carried over a USB 3.1 Gen 2 Type-C connection, with a maximum bandwidth of 10Gbps.

AppleInsider's testing of the drive using BlackMagicDesign's Disk Speed test put the 4TB model as having read speeds of 677MB/s, while write speeds were 756MB/s. While neither are quite at the 800Mb/s, it is in the ballpark. Both speed tests are still far faster than the sub-4TB models by a long way.

AppleInsider's speed test showed the Crucial X6 4TB is quite quick, but can thermally throttle.
AppleInsider's speed test showed the Crucial X6 4TB is quite quick, but can thermally throttle.


Over 50 sustained tests, we noticed that there was a drop in performance of around 15%. This is either a heat or cache "issue," but is acceptable for everyday use.

Compatibility and support

Unlike some other drives that include security features like onboard encryption, you're looking at a decidedly simpler device overall here. This isn't a high-security drive and is instead a block of storage you can plug in and access whenever and wherever you want.

That said, there's nothing stopping you from using various software-based tools for encryption and backup purposes. Crucial includes support for Apple's Time Machine, FileVault, BitLocker, and Windows Backup.

Naturally, it works with Macs and iPadOS devices, along with Windows, Android, and major game consoles.

In terms of support, you have a three-year warranty from the time of purchase.

Compact and capable

The Crucial X6 4TB Portable SSD is a great answer to the problem of needing extra external storage for your MacBook Pro or iPad Pro while on the move. Its small size, which is improved by reusing USB Type-C cables you may already own for other devices, makes it very easily carried around alongside your hardware.

If you're looking for something that is fully featured, offers enhanced security, and other extras, there are other drives on the market, and this wasn't ever intended to be your solution.

The included cable is short but usable, and doesn't add too much weight or size to the Crucial X6 package.
The included cable is short but usable, and doesn't add too much weight or size to the Crucial X6 package.


Those who want blistering speed at all times may also want to look elsewhere, as some Thunderbolt drives or external RAID enclosures can offer far faster speeds. That said, the speeds observed with the 4TB model are still more than enough for many potential users.

There are cheaper do-it-yourself solutions. You can save a couple of bucks at full retail to shell out around $360 for a 4TB SATA SSD and maybe another $25 for an external enclosure that connects over USB-C, for a total investment of just a bit less than $400. But, you're, you're going to be limited to the SATA bus speed of the DIY model at less than 550Mb/s, a few hundred below Crucial's drive, as well as lacking any of the protective elements.

The Crucial X6 4TB SSD is a no-frills drive, and it gets the job done. It does it without style, and at a good price to performance ratio.

Pros
  • Compact and light.
  • Fast connectivity over USB Type-C.
  • Reasonably priced.
  • Drop and knock protection.
Cons
  • Uninspiring design.
  • Heat throttles connectivity.
  • No extra encryption features.

Rating: 4 out of 5

Where to buy

The Crucial X6 4TB is available to buy at Amazon for $489.95. It can also be bought from B&H Photo for $489.95.

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Comments

  • Reply 1 of 8
    M68000M68000 Posts: 365member
    Thanks for this review,  good to know.  Love the use of the sharpie marker for size
  • Reply 2 of 8
    BEWARE! Not for media pro use. Write speed plummets after drive is only 20% full! The Crucial X6 4TB drive is not suitable for anyone who wants to fill up the drive with large file transfers, say anyone working in video / audio media for example. It uses a "dynamic cache" which means the size of the write cache shrinks as the drive fills up. It's the SLC write cache that can copy files at 800MB/sec. The true QLC write speed of the drive is around 80MB/sec - slower than most old school spinning HDDs. When the drive is new and empty, the SLC write cache size is about 800GB. So the first 800GB of data you copy onto the drive will go fast. If you do a Blackmagic Disk Speed Test, that's what you'll measure, the fast SLC cache. But as soon as you've copied 800GB of data, that SLC cache almost completely disappears. Instead of 800GB of cache, it quickly drops down to like 27GB of fast write cache. When I heard the drive had an 800GB write cache, I thought that would be fine, that I could copy 800GB of data, wait a bit for the cache to empty, then copy another 800GB at the same fast speed. But no, once you've filled the drive just 20%, the write cache drops to 27GB. (It might drop even further, but I didn't have the patience to continue filling the drive past 1TB at the 80MB/s QLC crawl!) So really the 4TB X6 drive has a small 27GB write cache, plus a ~775GB bonus cache that disappears after first use. The craziest part is - the dynamic cache never grows back, after first use you'll never get that 800GB cache back again! Even if you delete all the files you've ever copied onto the drive, and the drive looks empty in your OS, the write cache stays at 27GB, it never goes back up to the full 800GB. The only way I found to get the full original write cache size back was to do a complete secure erase format of the drive writing zeros across the entire capacity. As I wanted to use this drive for video editing, I wanted to quickly fill up the whole capacity with large file transfers. Not possible with this slow-writing QLC drive. The only good uses for this drive are say Time Machine backups, where you do a large initial backup then small incremental backups afterward. It would be okay for anyone who never plans to copy any files larger than 27GB at one time. The fact that I can't get the full cache size back even after deleting all the files makes me very suspicious of this drive. I say stay away. (I formatted my drive in APFS. I actually got an error message when I first connected my drive that it had unfixable partition errors with the factory exFAT formatting, and it would only mount ready-only in MacOS, so I had to format it. It's possible that the drive might behave a little differently with other disk formats, I don't know. Personally I need it to work with APFS. And I did try running the 'trimforce' command in MacOS Mojave, I did not see a difference in the drive performance.)
    maltzseanj
  • Reply 3 of 8
    Mike WuertheleMike Wuerthele Posts: 6,257administrator
    BEWARE! Not for media pro use. Write speed plummets after drive is only 20% full! The Crucial X6 4TB drive is not suitable for anyone who wants to fill up the drive with large file transfers, say anyone working in video / audio media for example. It uses a "dynamic cache" which means the size of the write cache shrinks as the drive fills up. It's the SLC write cache that can copy files at 800MB/sec. The true QLC write speed of the drive is around 80MB/sec - slower than most old school spinning HDDs. When the drive is new and empty, the SLC write cache size is about 800GB. So the first 800GB of data you copy onto the drive will go fast. If you do a Blackmagic Disk Speed Test, that's what you'll measure, the fast SLC cache. But as soon as you've copied 800GB of data, that SLC cache almost completely disappears. Instead of 800GB of cache, it quickly drops down to like 27GB of fast write cache. When I heard the drive had an 800GB write cache, I thought that would be fine, that I could copy 800GB of data, wait a bit for the cache to empty, then copy another 800GB at the same fast speed. But no, once you've filled the drive just 20%, the write cache drops to 27GB. (It might drop even further, but I didn't have the patience to continue filling the drive past 1TB at the 80MB/s QLC crawl!) So really the 4TB X6 drive has a small 27GB write cache, plus a ~775GB bonus cache that disappears after first use. The craziest part is - the dynamic cache never grows back, after first use you'll never get that 800GB cache back again! Even if you delete all the files you've ever copied onto the drive, and the drive looks empty in your OS, the write cache stays at 27GB, it never goes back up to the full 800GB. The only way I found to get the full original write cache size back was to do a complete secure erase format of the drive writing zeros across the entire capacity. As I wanted to use this drive for video editing, I wanted to quickly fill up the whole capacity with large file transfers. Not possible with this slow-writing QLC drive. The only good uses for this drive are say Time Machine backups, where you do a large initial backup then small incremental backups afterward. It would be okay for anyone who never plans to copy any files larger than 27GB at one time. The fact that I can't get the full cache size back even after deleting all the files makes me very suspicious of this drive. I say stay away. (I formatted my drive in APFS. I actually got an error message when I first connected my drive that it had unfixable partition errors with the factory exFAT formatting, and it would only mount ready-only in MacOS, so I had to format it. It's possible that the drive might behave a little differently with other disk formats, I don't know. Personally I need it to work with APFS. And I did try running the 'trimforce' command in MacOS Mojave, I did not see a difference in the drive performance.)
    I think you got a bad drive, and your formatting experience near the end of your post suggests that as well. We didn't have the same slowdown using APFS, and even after transferring 2TB of files at the 20% slower speed we cited in the piece, we never, ever went down to your 80 megabytes per second speed, which is sub-spinning drive speed.  

    And a transfer immediately after, repeating the 2TB, very obviously demonstrated a clear write cache.

    I wouldn't use this drive for video editing or a scratch drive. But for a fast data repository? Sure.
    edited July 5 muthuk_vanalingam
  • Reply 4 of 8
    flydogflydog Posts: 1,005member
    BEWARE! Not for media pro use. Write speed plummets after drive is only 20% full! The Crucial X6 4TB drive is not suitable for anyone who wants to fill up the drive with large file transfers, say anyone working in video / audio media for example. It uses a "dynamic cache" which means the size of the write cache shrinks as the drive fills up. It's the SLC write cache that can copy files at 800MB/sec. The true QLC write speed of the drive is around 80MB/sec - slower than most old school spinning HDDs. When the drive is new and empty, the SLC write cache size is about 800GB. So the first 800GB of data you copy onto the drive will go fast. If you do a Blackmagic Disk Speed Test, that's what you'll measure, the fast SLC cache. But as soon as you've copied 800GB of data, that SLC cache almost completely disappears. Instead of 800GB of cache, it quickly drops down to like 27GB of fast write cache. When I heard the drive had an 800GB write cache, I thought that would be fine, that I could copy 800GB of data, wait a bit for the cache to empty, then copy another 800GB at the same fast speed. But no, once you've filled the drive just 20%, the write cache drops to 27GB. (It might drop even further, but I didn't have the patience to continue filling the drive past 1TB at the 80MB/s QLC crawl!) So really the 4TB X6 drive has a small 27GB write cache, plus a ~775GB bonus cache that disappears after first use. The craziest part is - the dynamic cache never grows back, after first use you'll never get that 800GB cache back again! Even if you delete all the files you've ever copied onto the drive, and the drive looks empty in your OS, the write cache stays at 27GB, it never goes back up to the full 800GB. The only way I found to get the full original write cache size back was to do a complete secure erase format of the drive writing zeros across the entire capacity. As I wanted to use this drive for video editing, I wanted to quickly fill up the whole capacity with large file transfers. Not possible with this slow-writing QLC drive. The only good uses for this drive are say Time Machine backups, where you do a large initial backup then small incremental backups afterward. It would be okay for anyone who never plans to copy any files larger than 27GB at one time. The fact that I can't get the full cache size back even after deleting all the files makes me very suspicious of this drive. I say stay away. (I formatted my drive in APFS. I actually got an error message when I first connected my drive that it had unfixable partition errors with the factory exFAT formatting, and it would only mount ready-only in MacOS, so I had to format it. It's possible that the drive might behave a little differently with other disk formats, I don't know. Personally I need it to work with APFS. And I did try running the 'trimforce' command in MacOS Mojave, I did not see a difference in the drive performance.)
    https://www.baconediting.com/blog/let-your-ideas-flow-the-importance-of-paragraphs
  • Reply 5 of 8
    maltzmaltz Posts: 275member
    BEWARE! Not for media pro use. Write speed plummets after drive is only 20% full! The Crucial X6 4TB drive is not suitable for anyone who wants to fill up the drive with large file transfers, say anyone working in video / audio media for example. It uses a "dynamic cache" which means the size of the write cache shrinks as the drive fills up. It's the SLC write cache that can copy files at 800MB/sec. The true QLC write speed of the drive is around 80MB/sec - slower than most old school spinning HDDs. When the drive is new and empty, the SLC write cache size is about 800GB. So the first 800GB of data you copy onto the drive will go fast. If you do a Blackmagic Disk Speed Test, that's what you'll measure, the fast SLC cache. But as soon as you've copied 800GB of data, that SLC cache almost completely disappears. Instead of 800GB of cache, it quickly drops down to like 27GB of fast write cache. When I heard the drive had an 800GB write cache, I thought that would be fine, that I could copy 800GB of data, wait a bit for the cache to empty, then copy another 800GB at the same fast speed. But no, once you've filled the drive just 20%, the write cache drops to 27GB. (It might drop even further, but I didn't have the patience to continue filling the drive past 1TB at the 80MB/s QLC crawl!) So really the 4TB X6 drive has a small 27GB write cache, plus a ~775GB bonus cache that disappears after first use. The craziest part is - the dynamic cache never grows back, after first use you'll never get that 800GB cache back again! Even if you delete all the files you've ever copied onto the drive, and the drive looks empty in your OS, the write cache stays at 27GB, it never goes back up to the full 800GB. The only way I found to get the full original write cache size back was to do a complete secure erase format of the drive writing zeros across the entire capacity. As I wanted to use this drive for video editing, I wanted to quickly fill up the whole capacity with large file transfers. Not possible with this slow-writing QLC drive. The only good uses for this drive are say Time Machine backups, where you do a large initial backup then small incremental backups afterward. It would be okay for anyone who never plans to copy any files larger than 27GB at one time. The fact that I can't get the full cache size back even after deleting all the files makes me very suspicious of this drive. I say stay away. (I formatted my drive in APFS. I actually got an error message when I first connected my drive that it had unfixable partition errors with the factory exFAT formatting, and it would only mount ready-only in MacOS, so I had to format it. It's possible that the drive might behave a little differently with other disk formats, I don't know. Personally I need it to work with APFS. And I did try running the 'trimforce' command in MacOS Mojave, I did not see a difference in the drive performance.)

    Thanks, that's the sort of information I really look for in a storage review.  Most of the rest I can get in the spec sheet.  lol  I do have a question, though...

    "do a complete secure erase format of the drive writing zeros across the entire capacity"

    For an SSD (and actually other drives) a "secure erase" has a fairly specific meaning, and it isn't "writing zeros across the entire capacity".  Can you clarify the process you're talking about here?  Does this device support TRIM (on Macs or any other OS) and can you do an ATA Secure Erase (or an NVMe Format)?

  • Reply 6 of 8
    Mike WuertheleMike Wuerthele Posts: 6,257administrator
    maltz said:

    Thanks, that's the sort of information I really look for in a storage review.  Most of the rest I can get in the spec sheet.  lol  I do have a question, though...

    "do a complete secure erase format of the drive writing zeros across the entire capacity"

    For an SSD (and actually other drives) a "secure erase" has a fairly specific meaning, and it isn't "writing zeros across the entire capacity".  Can you clarify the process you're talking about here?  Does this device support TRIM (on Macs or any other OS) and can you do an ATA Secure Erase (or an NVMe Format)?

    TRIM on Windows, no problem. Media is not NVMe, nor is the drive. ATA secure erase works.

    And, I'm not sure what the poster's issue was with the write cache, and I think he's talking about the sub-4TB versions which are engineered differently and are slower, as these have just shipped.

    A write cache that never empties is a problem which isn't duplicated here -- but the larger problem for the poster is the failure to format from the jump form exFAT, which suggests a bigger problem.
    edited July 5 maltz
  • Reply 7 of 8
    Thanks for your replies. I hope for everyone else’s sake that my drive was a lemon and Crucial makes better SSDs than that. No, I definitely was referring to the 4TB model, I wouldn’t even touch the slower SATA speeds on the 2TB sizes and below. Just sharing my experience, I really wanted to like this drive because it seemed like such a good deal. But it turns out there’s a reason it’s the cheapest 4TB SSD you can get. 

    I returned mine to Amazon and didn’t bother trying to get a replacement, I just decided to avoid QLC drives in the future. Unfortunately after doing more research on QLC drives I do think my experience is typical of this type of drive, although my use case might be less common. QLC flash does have slow native speeds in the 80-100MB/sec range, according to many articles, and must rely on SLC cache for faster peak speeds. (Yes that is slower than most spinning HDDs and I agree that is absurd!)  Tom’s Hardware notes that the Crucial X6 does use a dynamic SLC cache but doesn’t specify the size. When researching dynamic cache SSDs, I found for example the Intel 660p SSD (which uses QLC and a dynamic cache) and official materials from Intel show how it’s designed with a cache size that shrinks as it fills up. Although not as dramatically as what I experienced on the Crucial X6. My speed testing was done using the great program CopyQueue which can show a real time readout of file transfer speeds, I use it almost daily in my work for moving around large media files and trust its results. 

    The cache speeds did recover after waiting a bit after a transfer and doing another transfer, but the total amount of cache shrank over time as I described. After copying 1TB of data, then waiting a bit, the next 27GB of data would copy quickly. But more data beyond that would slow way down again. Watching the file transfer slow down after a certain amount of GBs had copied, repeatedly, is how I could observe when the SLC cache had filled up. Without a file copy program with a real time speed indicator, one wouldn’t be able to measure the slowdown as easily. Check the negative reviews on Amazon for the 4TB X6, and you’ll see some other people with similar experiences. Like the Intel chart says below, average users might not have a ton of data, so a lot of people probably wouldn’t run into these issues as often as someone who regularly needs to move around multiple TBs of video files. Like I said, it could be ok for Time Machine, an average person’s documents and photos, any usage where sustained write speed for large files isn’t a top priority.

    To the question of what I meant by secure erase, I used the “Security Options” feature in Disk Utility when reformatting the drive and moved the slider one stop over from the left, the fastest option that said it would overwrite the whole drive. Doing that did seem to restore the cache size to how it was out of the box. I formatted the drive in APFS immediately before first using it, as I always would with any new drive, and also there was a problem with the factory ExFAT formatting apparently since MacOS gave an error that said it would be read only until reformatting. When I found it slowed down after the first 800GB of data copied, and how the cache size seemed to stay so much smaller afterward, I tried the reformat with secure erase option as a last resort. Then it seemed to work like new again, although again the cache size seemed to shrink unrecoverably after starting to fill up the drive. That’s when I returned this drive and started shopping around for something else.

    It’s a shame because Amazon had these on crazy discount for Prime day, if it worked better I would have bought a few more!

    Instead I picked up a few smaller Sandisk Extreme V2 and WD My Passport (2021) SSDs and they have been great. Their speeds stay much more consistent throughout large file transfers. Actually the WD My Passport has faster sustained writes (~900MB/s) than the Sandisk Extreme (~800MB/s) although it is cheaper, and reviews said the Sandisk was faster. I only wish they had 4TB options closer in price to the X6.

    (Also ha ha I do love paragraph breaks too, I wish the site’s default comment box didn’t strip them out!)


    edited July 5
  • Reply 8 of 8
    beowulfschmidtbeowulfschmidt Posts: 1,430member
    Yes, many (if not all) QLC drives have a known issue with slowing down when a large amount of data is copied to the drive at once, whether that be a single large file or multiple small ones.  When the cache fills up, the operation, while initially quite fast, then proceeds at roughly the speed of the main "drive".

    Finish copying the large amount of data, let the cache flush, and the next large data that's copied will exhibit the same behavior, initially fast, then slowing down.
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