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

Thanks for this review,  good to know.  Love the use of the sharpie marker for size

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.)

atonaldenim said:

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.

atonaldenim said:

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

atonaldenim said:

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)?