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I am faced with the following scenario: I have one SSD from which the OS runs off of and one usb 3.0 flash drive and a 7GB file I want to copy from the SSD to the flash drive. The file is downloaded from a website hosted on my university campus.

If I want to copy it straight from the ssd to the drive, I get around a max of 5 MB/s copy rate but on average probably 2 MB/s. I understand that even if it says it's 3.0 it may not reach the maximum possible speed because of bandwidth bottlenecks caused by idiotic drivers, chipsets, cheap flash memory or controllers, yada yada yada, but explain this: if I try to download the file straight to the drive I get around 25 to 30 MB/s download speed.

So essentially, it is 6 times faster to download it again from scratch straight to the drive than it is to copy it from the SSD to the same drive (and yes, I actually timed it, just to be sure). The question is, why?

If I did not try this, I would have assumed that the drive is simply slow, but it clearly can have write speeds a lot faster than 5 MB/s since I can download straight to it with 30 MB/s. Also, I understand that copying it from the SSD implies that I am limited by the SSD read speed, but it's a freaking SSD that boots windows in 4 seconds, how slow of a read speed can it have that it limits me to an apparent max speed of 5 MB/s copy rate ?!

What gives?

  • You could check with Task Manager to see if it’s actually writing that fast when you download to the flash drive directly. It could instead be buffering differently. – Daniel B Dec 17 '17 at 15:42
  • Just as I have said, I actually timed it and it works out to around 22 MB/s, not quite the 30 MB/s that the browser reported, but still a lot faster than what windows explorer is capable of. – user1969903 Dec 17 '17 at 15:44
  • Caching somewhere implemented by the campus? Did you try to download in the reverse order; download to USB first, then redownload to SSD? – Damon Dec 17 '17 at 15:57
  • This sounds a lot like transparent caching going on. If you re download the file to your ssd do you get the fastest speed? Try it twice to be sure. – Mokubai Dec 17 '17 at 16:14
  • I just tried it. Downloading either to the SSD or to the flash drive seems to take pretty much the same amount of time, give or take 30 seconds, regardless of the order. I cleared the browser cache and used a different browser too, with the same result. I also reformatted the drive before each test. As for the campus, I'm not sure whether they do implement any caching. – user1969903 Dec 17 '17 at 16:34

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