USB Flash drive - very slow writes, but read speeds are fine

Bree · 03 Jul 2021

Suddenly one of my USB Flash drives has become very slow to write to. I'm seeing 'peak' write speeds measured in KB/sec, not MB/sec. However, there are no write errors, and once written files can be read at normal speeds. All my other USBs work normally, just this one is slow, and it's the same in every PC and OS I have, Win10 or Win7.

USB Flash drive - very slow writes, but read speeds are fine-usb-very-slow-writes.png

Obviously there's something very wrong with this particular PNY 32GB USB 2.0 flash drive. But intriguingly it passes every test I can throw at it, bar the write speed. I have installed Ventoy on it and added ISOs for Minitools bootable Partition Wizard 9.1 and Windows 10 21H1, the latter taking over 20 hours to copy!. But both boot successfully. And when I booted Partition Wizard from this USB, its surface check of the USB then said 100% good.

I've never has a USB fail on me before, and certainly not heard of one failing like this.

I'm not looking for repair suggestions, I'll dump this USB soon. But I'm intrigued, can anybody suggest a test that will reveal what's actually gone wrong?

Anibor · 03 Jul 2021

Old age. No more "new" cells, must erase and then write.

W10 Tweaker · 03 Jul 2021

Hi Bree,

Have you tested the write speed with disk cache enabled?

How about drivers, is it possible the old drivers don't like the current OS?

Bree · 03 Jul 2021

W10 Tweaker said:

How about drivers, is it possible the old drivers don't like the current OS?

Drivers are not likely as the cause. This usb (and only this one) has slow writes whatever PC it's used on, whichever port it's in (usb 2 or 3) and whatever OS is installed (Win7 or Win10).

Anyway, it's deteriorated further now to the point where it's unusable in any machine. Any operation, such as Diskpart's CLEAN, results in the device disappearing, then returning as an unrecognised device. Definitely was a dying usb, and is now quite dead.

USB Flash drive - very slow writes, but read speeds are fine-image.png

Marking the thread as solved - in the sense that further investigation is impractical.

W10 Tweaker · 04 Jul 2021

Too bad, that might have been an interesting adventure.

MisterEd · 04 Jul 2021

I know you can't go further because your flash drive no longer works but I wanted to mention my experience.

I have a: PNY Compact Attache 64GB (USB 2.0). I was never happy with it even when it was new because it seemed slow. Running CrystalDiskMark shows why. Both random write tests gave 0.00 MB/sec.

USB Flash drive - very slow writes, but read speeds are fine-pny2.jpg

Compare that with this flash drive: SanDisk Cruzer Glide USB 16GB (USB 2.0)

USB Flash drive - very slow writes, but read speeds are fine-sandisk-16gb-1.jpg

Also, compare that with this flash drive: SanDisk Ultra 128GB (USB 3.0).

USB Flash drive - very slow writes, but read speeds are fine-sandisk2.jpg

Mooly · 06 Jul 2021

How strange you should just have posted this as I'm faffing with one now.

I've experienced this on at least two occasions and like you, never found a reason why. One common factor though seems to be that the drives in question have been used in systems that have had them powered up continuously.

First time was a Sandisk USB 3 64Gb in a Sony Android TV. When I came to use the drive on a PC it would write at at just a few kb speed. I tried diskpart and clean and create new partitions etc. No good. Sandisk replaced it as it had a 5 yr warranty. The Sony does write its own file system header on a drive but I fixed all that with Diskpart.

Second time was a Sandisk (is there a pattern here) 64Gb USB2 drive that was connected to my BT Hub for 18 months and used as a network location for file history. New Hub, repurposed the drive and popped in the PC. Slow slow slow. Tried diskpart but no good. A 10 year old TDK drive is more than ten times faster.

Third drive is a (ho hum... there is a pattern) SanDisk 16Gb Cruzer Edge and that now will not get recognized correctly. It will not show in File Explorer unless you repeatedly remove and replace it (contacts clean and good) and yet it shows in 'Remove Hardware'. I can even get to that little window that says 'This device is working correctly'.

Bree · 06 Jul 2021

Thank you @Mooly for your input.

I use mine like I used to use floppy disks. They get plugged in/out frequently, written to (and re-written) a lot. I have amassed quite a collection now and this is my first to have died.

I was expecting that a dying usb would go read-only first, or so I have heard. Thanks for confirming that 'write slowly' is another observed failure mode.

None of my USBs are left plugged in for any length of time, so that's not a factor in my case. I tend to buy multi-packs of known brands (Lexar, Sandisk, Toshiba, etc.) from retail shops (never from online) whenever I find them at a discount. None of my Sandisk have ever given me a problem.

My oldest usb is a 1GB 'Udisk 2.0' (quite large for its time, which tells you its age), my next oldest are a bunch of Sandisk Cruzer Edge 4GB. All those are still working well.

Edit: in researching this subject I came across this useful site from Nirsoft, where you can look up the real-world speed tests for many USBs. It still includes results for many really old USBs, including those I mentioned above.

USB Flash Drive Speed Tests - VID = 781 (SanDisk Corp.), PID = 556b

Mooly · 06 Jul 2021

Some useful info in the link

I think I'm going to get a few replacement drives and start afresh. Backups of data are just to important to risk anything going amiss.

One think I read today and I'm not sure if there is any truth to it is that you should not format a new drive that had preinstalled recovery software on it (as many do) because it can interfere with the alignment of blocks when you come to write to it. I suppose a bit like when we first started using SSD's and used to check that they were aligned correctly.

Good to hear your experience of Sandisk experience has been good.

MisterEd · 06 Jul 2021

Bree said:

Edit: in researching this subject I came across this useful site from Nirsoft, where you can look up the real-world speed tests for many USBs. It still includes results for many really old USBs, including those I mentioned above.

USB Flash Drive Speed Tests - VID = 781 (SanDisk Corp.), PID = 556b

Mooly said:

Some useful info in the link

I think I'm going to get a few replacement drives and start afresh. Backups of data are just to important to risk anything going amiss.

One think I read today and I'm not sure if there is any truth to it is that you should not format a new drive that had preinstalled recovery software on it (as many do) because it can interfere with the alignment of blocks when you come to write to it. I suppose a bit like when we first started using SSD's and used to check that they were aligned correctly.

Good to hear your experience of Sandisk experience has been good.

The tests use USBDeview. The shortcoming of it is that it only tests sequential read and write operations. When using multiple small files, the read/write performances are usually much lower than sequential read/write.

The two PNY flash drives I have when tested with CrystalDiskMark show poor random writes speeds. Since USBDeview does not test random read/writes this is missed by it.

Of course no manufacturer of flash drives or SSDs likes to talk about the random read/write speeds. They only talk about the sequential read/write speeds because the random speeds are poor in comparison.

Even though the random read/write speeds are not talked about, in general if the sequential read/write are good then I expect the drives to be better than those which don't have any performance values listed at all.

I wised up years ago and stopped buying flash drives that did not list any performance values. That included those made by PNY. I have since only bought flash drives made by SanDisk.

I had thought about buying one of these flash drives because reviews showed them quite fast:
SanDisk Extreme PRO USB 3.2 Solid State Flash Drive (128GB, 256GB, 512GB, 1TB)
Sequential Read Performance: Up to 420MB/s, Sequential Write Performance: Up to 380MB/s

However, I now have a spare 512GB M.2 NVME SSD, 512GB M.2 SATA SSD, and a 256 M.2 SATA SSD. Because I was cloning drives I also have a M.2 NVME SSD enclosure and a M.2 SATA SSD enclosure. That makes a large capacity flash drive unnecessary.

In any event I don't recommend USB flash drives for long term storage. USB SSD drives are much more reliable for that. Even though both flash drives and SSDs use flash memory SSDs have internal electronics that maximizes their longevity.

A number of years ago I remember reading about someone that installed Linux on a flash drive. The drive failed after about 30 days.

Just like flash drives I don't recommend anyone buy cheap no-name SSDs. Of course, it depends upon how important you think the information you put on them is. BTW, I saw some really cheap SSDs on Wish.com. You know what they, "If it's too good to be true then it probably isn't".

I have not read anywhere that said it was better not to reformat a new drive that had preinstalled recovery software. I suppose it is possible that they are using a special format that optimizes the drive for backup purposes. If they did then that format program should be available for download so that the user could reformat the drive if they wanted.