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Transfer Speeds Suddenly Slowing Down when transferring large files between SSDs

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Anyone know why my file transfer speed suddenly drops from 292 MB/s to 83 MB/s after awhile.

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RjL190365Correct answer

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That is typical of some external USB 3.2 Gen 1x1 SSDs, which are based on budget SATA designs. And in your case, you have depleted the external SSD's Turbo write cache, and the true write speed of the SSD in question comes into play. Some of those budget SSDs can't sustain even 100 MB/s in sequential writes when the SLC cache is depleted! That's barely faster than a spinning HDD!

I noticed this slowdown in sequential transfers on my main system's internal m.2 NVMe Samsung 980 PRO SSD, whose write speed (of both the 1 TB and the 2 TB capacities) dropped from 5000 MB/s all the way down to about 1600 MB/s after about 12 TB or writing.

And it is because these drives all use TLC or QLC NAND flash memory. In fact, your particular external SSD uses QLC chips.

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RjL190365

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Oh, by the way, which 1 TB SanDisk external SSD model do you have? Not all external SSDs from the same brand are created equal. In fact, if your SanDisk external SSD is not the Extreme or the Extreme Pro, then you just have a lousy performer of an external drive. (The giveaway is the color of the retail box that it came in: The lousy ones come in a red box, while the bExtreme's come in a black box.)

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mPatipadaAuthor

Participating Frequently

Oh wow, my one came in a RED box. Thanks a lot for explaining the situation

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RjL190365

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You're not alone in choosing the wrong external SSD for the job. That SSD is perfectly fine for smaller files that do not get a chance to fully saturate the SSD's small (about 5 GB) turbo write cache. But then again, that's the very same purpose for the many USB thumb/stick/pen drives out there.

And even my particular SanDisk Extreme v2 external SSD has a cache-depleted true sequential write speed of about 800 MB/s. Not the fastest external drive out there, but it's close to the drive's advertised 1050 MB/s maximum transfer speed.

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RjL190365Correct answer

Legend

That is typical of some external USB 3.2 Gen 1x1 SSDs, which are based on budget SATA designs. And in your case, you have depleted the external SSD's Turbo write cache, and the true write speed of the SSD in question comes into play. Some of those budget SSDs can't sustain even 100 MB/s in sequential writes when the SLC cache is depleted! That's barely faster than a spinning HDD!

I noticed this slowdown in sequential transfers on my main system's internal m.2 NVMe Samsung 980 PRO SSD, whose write speed (of both the 1 TB and the 2 TB capacities) dropped from 5000 MB/s all the way down to about 1600 MB/s after about 12 TB or writing.

And it is because these drives all use TLC or QLC NAND flash memory. In fact, your particular external SSD uses QLC chips.

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Peru Bob

Community Expert

Check Task Manager to see what is using resources.

Are there any programs running in the background?

How full are the drives?

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mPatipadaAuthor

Participating Frequently

This happens as a routine thing when transffering large files. It had around 500GB free space when this happened(SanDisk 1 TB prtable SSDs). Are you aware of something like this happening in Windows 10 ? I thought it maybe a common issue. @Peru Bob

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