Less than 2 months ago, I ordered a thumb drive (cheap one). I used it the day it arrived and I think about 3 days after that. Merely checked it with badblocks and then dd-ed a Linux image into it. It sat on a tray since and wasn't touched.

When I connected it today, I wanted to first check the integrity of the image on it. Didn't check out as I always got input/output errors when trying to read from the thumb drive:

$ sudo dd if=/dev/sdb of=/dev/null bs=1M
dd: error reading '/dev/sdb': Input/output error
162+1 records in
162+1 records out
170524672 bytes (171 MB, 163 MiB) copied, 7.75699 s, 22.0 MB/s

$ sudo dd if=/dev/sdb of=/dev/null bs=1M
dd: error reading '/dev/sdb': Input/output error
74+1 records in
74+1 records out
78381056 bytes (78 MB, 75 MiB) copied, 3.81105 s, 20.6 MB/s

$ sudo dd if=/dev/sdb of=/dev/null bs=1M
dd: error reading '/dev/sdb': Input/output error
22+1 records in
22+1 records out
23461888 bytes (23 MB, 22 MiB) copied, 1.45307 s, 16.1 MB/s

$ sudo dd if=/dev/sdb of=/dev/null bs=1M
dd: error reading '/dev/sdb': Input/output error
41+0 records in
41+0 records out
42991616 bytes (43 MB, 41 MiB) copied, 2.30087 s, 18.7 MB/s

$ sudo dd if=/dev/sdb of=/dev/null bs=1M
dd: error reading '/dev/sdb': Input/output error
37+1 records in
37+1 records out
39321600 bytes (39 MB, 38 MiB) copied, 2.16684 s, 18.1 MB/s

The weird thing is that it always fails in different spots. Even managed to read over 300 MiB once, I think (16 GB thumb drive) (but I didn't check whether the read data was correct unfortunately).

Broken thumb drive. Who cares, right?

I then got curious and wanted to see when writing failed, just for the heck of it before throwing it way. The weird thing is: It didn't. I merely dd-ed /dev/zero onto it. After being surprised by this behavior, I dd as many 1 MiB blocks back from the stick as possible and piped them into sha256sum. Not only did I not receive an input/output error, but the sha256sum of it also checked out with the sha256sum taken directly from /dev/zero (with the same number of blocks).

After being surprised by this behavior, I unplugged it for 3 hours and ran badblocks on it: https://pastebin.com/y5SATDQq

I'm very surprised by this behavior. Why is this?

Regarding the close vote: I'm running this on it and will edit this question after it finished. I don't think it's economically viable to fake 16 GB thumb drives, these days. I bought an obviously fake one (allegedly 128 GB or 256 GB or something like that but way too cheap for that to be true) once (for experimenting) and it turned out to actually be a 16 GB thumb drive. Plus, this one has over 1'500 reviews on Amazon and an average of 4 out of 5 stars. And it is sold by the manufacturer itself (Intenso).


Okay, this one failed: https://pastebin.com/xZ5VRpf2

But I then created an ext4 file system on the thumb drive and did this: https://pastebin.com/P1CCsDJT

The pastebin paste contains comments as to what I did to figure this out.

It read more than half the data back correctly and therefore can't be a fake thumb drive. In fact, only a single 1000 MiB block was corrupted. It can't be a fake thumb drive.

  • What is the most data you have written to the device? – Ramhound Jun 8 '17 at 11:51
  • @Ramhound I merely used badblocks (write mode) on it and then dd-ed the official ubuntu-16.04.1-desktop-amd64.iso onto it. I'm not entirely sure whether I did this. But that's definitely it. I didn't put any other data on it, yet. – UTF-8 Jun 8 '17 at 11:58
  • 1
    Possible duplicate of How is the capacity of a harddisk faked? – Burgi Jun 8 '17 at 12:07

Make sure you look over the amazon site again it actually is not sold by Intenso thats just linking the brand name if you look about halfway down the page it says Shipped and Sold by Amazon. Either way if you confirm its broken and not fake call Amazon for a replacement or if it actually turns out to be fake I'd call up Amazon tell them that they have been scammed and you by proxy have been scammed also.

Even if its really cheap and not worth shipping back still call them, as I find they often will just send you a replacement if your a good customer.

  • Thanks. But I'm not here because of the few euros that thumb drive cost. That money wouldn't have been worth writing the long text. I'm here to understand how the thumb drive's behavior can be explained. – UTF-8 Jun 14 '17 at 20:37

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