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I purchased a SanDisk Extreme Go 64GB USB flash drive about 2 months ago.

Out of the box, it performed as advertised, with 4k r/w being really good. Since it was faster than my HDD, I decided to use it as an everyday booting device for Windows 10.

I recently noticed that my system was unusually not responding, so I check the write speeds on the drive and they have fallen dramatically.

When writing, active time would reach 100 percent and task manager would display writing speeds between 4 kb and 100 kb.

I am aware that once flash memory cells have all been written to, the write speeds slow down. So, I tried multiple methods in hopes of performing a "Secure Erase" on the flash drive.

  1. Bitlocker Encryption
  2. ATA Secure Erase Command (wasn't supported)
  3. A tool SanDisk officially recommends, HP USB Formatting Tool ( took 6 hours )
  4. Cmd.exe "Clean all" command

After performing these, the drive would be reasonably fast for the first bit after I write data to it. However, these results were inconsistent which led to the conclusion that nothing had really done anything.

I assume the cells have been all written to for a while before I noticed this slow down ( had to reinstall windows completely a few times ), making me wonder if something else went wrong.

If anyone has any other ideas about what I could try to perform a Secure Erase or if anything else could be wrong, please share this information with me.

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3 Answers 3

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What is happening here is that you are seeing the erase speed of flash memory. Writing is fast but you can only write to an empty page and erasing is as you have discovered very slow. This is handled by actually having more memory on the device than the label says, the device has a pool of empty pages to be used for writing. A page is taken from the pool, written and put in place of the old page which is put in a pool of pages to be erased. The device erases those pages and moves then into the pool of writable pages.

So long as you don't write too fast this process is effectively invisible to the user. However, if you write too much the pool of empty pages is depleted and the write stalls until a page has been erased and added to the pool.

Note, also, that internally all writes are in pages no matter how small a piece of data you wrote. This can drive the reported write rates even lower.

These issues are inherent in the technology, you can't get around them. SSDs cost more because they're designed to work around it to a far greater degree.

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  • Thank you for this insight, this is exactly what I was looking for. Interesting how this process works. Aug 1, 2020 at 1:53
  • If I were to unallocate 10 GB of space from the flash drive, do you think this could have a positive effect in any way? Aug 1, 2020 at 2:29
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    @AlberichDrago That's one of the ways SSDs handle it better--TRIM support. The OS tells the drive what's unallocated, the drive can take those pages, wipe them and put them in the ready pool, thus making the ready pool a lot larger than it came from the factory. Flash drives don't support that, nothing you do at the file system or partition level can help. Aug 1, 2020 at 2:32
  • Still, this proves “SSDs cost more because they're designed to work around it to a far greater degree.” as the flash drive was noticeably cheaper. Aug 3, 2020 at 20:39
  • Do you deny that more time is spent working on the controller in SSDs? This is why they cost more, as the saying goes, "Time is Money". Simply denying that it costs more to produce SSDs than simple flash drives is very wrong from a manufacturing perspective. Jan 7, 2021 at 20:12
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There can be a lot of reasons for the slow down, but in my opinion the primary is that you are using it as a system disc, which is not the best use for a USB stick (especially if you use it heavily).

My advice is to buy a SATA SSD or (if your PC has an NVMe slot) to buy a NVMe SSD.

For (almost) the same price of your USB stick you can buy a 240 GB SATA SSD (just bought one yesterday) and enjoy a 500 MByte/sec speed.

USB sticks are great for copying data, doing backups, but if you use it "heavily", have a look to something more appropriate ;)

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  • Thank you for your response, however I am trying to get the most out of this $30 Purchase, and try to somewhat "fix" this flash drive. Jul 31, 2020 at 17:44
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    This answer is about as good as you will get. You really just picked the wrong medium for the task.
    – Tetsujin
    Jul 31, 2020 at 18:14
  • This answer may be a good answer, however it is not a solution to my problem. I'm not looking for a device to boot from, I am trying to erase the memory blocks on a flash drive. Jul 31, 2020 at 18:19
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    What do you mean fix it? Format the USB and scan it for bad blocks. If it doesn't recover it's speed on windows/Linux it has been permanently damaged. Return to square one and buy another, as this answer says, use the correct media for the job, USB flash drives were not designed for this use.... Jul 31, 2020 at 19:24
  • Can you please provide proof to support your comment? Would be nice to see some of the science behind this so I can understand it better :) Jul 31, 2020 at 22:26
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Having also several SanDisk flash drives and seeing the same effect, I still have a different answer:

The flash drive has two types of flash memory: One is a rather small, but fast "cache-like" memory, while the other is big, but slow.

What I saw when writing to a new stick was:

First the write rate was something like 140MB/s, but after a few seconds it dropped to about 7.5MB/s (the "USB 3.2" generation).

Partial screen shot showing copying progress in Windows 10

The older "USB 3.0" generation had about half of the speed (3-4MB/s).

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  • In this case the answer is clearly the fact OP was running OS from the USB flash drive which it is not designed for. Dec 2, 2022 at 12:39

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