Question USB flash drive write speed fast at the beginning then slows

Jan 9, 2020
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This issue is essentially the same as USB Transfer Speeds Mystery but that thread is not open for further replies.

My setup
Corsair Flash Voyager GTX 1 TB
Lenovo T470 and T480 computers, both with internal SSD's
Windows 10 on both
Copying a 100 or 300 GB TrueCrypt file from the internal SSD to the USB stick

Issue
Write speeds to start at 300 MB/s - fantastic.
Speed slows to 60-90 MB/s after a few minutes.

If I pause the transfer and resume, the speed briefly spike back up before quickly returning to the slower speed.


Attempted fixes
I had an issue with another manufacturer's USB stick write speed last year which was tied to it being formatted exFAT instead of NTFS. My Voyager was already formatted NTFS, but I tried exFAT anyway. Speeds were still slow after a few minutes.

It seemed like the write speeds stayed fast longer on the first try of the day but got slower in less time if I retried copies. The Voyager gets warm to the touch during these writes. Thinking perhaps it was related to heating, I tried to cool the Voyager but this didn't help.

I've searched other forums which had several suggestions:
Am I using USB 3.X not 1.0/2.0? Yes.
Tried different USB ports? Yes.
Is it just the cache running out? Clearly not if the transfer speed is fast for a few minutes at 300 MB/s.
I've tried disabling write cache on the drive.
Do I have a background process or antivirus slowing things down? ?Not that I can see - the Task Manager shows relatively low CPU and memory utilization. I've also tried booting into safe mode.
I've tried two computers.

Corsair claims 190-470 MB/s max write speed. The single file I'm using should be much faster than many small files.

Corsair support has offered a hardware swap under warranty, but isn't admitting a known hardware problem. Frankly, I'm doubting this would be fixed by simply replacing the drive.

I haven't exhaustively updated drivers, BIOS, etc. I was hoping for some guidance before investing a lot more time.

Thanks in advance for the help.
 
Jan 9, 2020
2
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10
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This is absolutely normal for these devices.
The cache fills up, and speed drops.
Please explain further. It isn’t clear to me how cache explains what I’m seeing. Even just 1 minute (shorter than the time my drive sustains 300 MB/s before slowing) would be 18 GB of writing. Caches are much smaller than that, so why does the write speed slow after minutes of sustained high write speed?
 

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