07 - All about 'Fake' SD cards and USB Flash drives

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NEW! FakeFlashTest.exe - test your suspect 'fake' SD card or USB Flash drive in just a few minutes (rather than hours!) - read my blog.

FakeFlashtest Downloads are at bottom of this page.

Note: Some people have found that the FakeFlashTest Quick Size Test fails all the devices that they test.
This seems to be due to something that has been install in Windows (e.g. Anti-Malware or Anti-Virus software or perhaps a driver).
If you reboot Windows in Safe Mode (press SHIFT key whilst clicking on Restart) and run FakeFlashTest in Safe Mode, the Quick Size Test should work correctly.

I have put a lot of hours of hard work into FakeFlashTest and it is totally free
<- If FFT has saved you from a disaster, please consider making a small  donation, it would be much appreciated!

SD Insight SmartPhone app for SD cards

You can download the free Android app SD Insight from the Google Play App Marketplace which will reveal the manufacturers pre-programmed details of your SD card. This does not actually test the card, but it can give a good indication of whether the card is genuine or not.

There is also a Google Play free app. called 'SD Card Tester' that will write a large file to your SD card (slowly!) and read it back here (note: double-tap to change folder).

See here for many examples of fake SD cards and how to visually check one.

What is a 'Fake Capacity' USB Flash Drive or SD card?

Many USB flash drives and SD cards are being sold on eBay and other auction sites at very cheap prices (too cheap!). These USB pens are usually of a high capacity (16, 32GB, 64GB or 128GB) and usually from the Far East, but some UK sellers also sell these too. 98% of these sellers are selling 'fake' USB Flash drives (fake UFDs) - either knowingly, unknowingly or I-don't-really-want-to-know-ingly!

The two types of 'Fake' 16GB USB Flash Drives

Most Flash drive and SD cards are pre-formatted as FAT32. The directory and file names on a FAT32 device are all located in the first few MBs at the bottom of memory. 
The actual file contents (data) are stored above the directory.

It is similar to how a book library uses library cards. The library cards are stored at the bottom of memory and the actual books are stored higher up in memory.
If you destroy the library cards, then you (Windows, linux, your camera/smartphone) cannot find any of the books.

2MB+ Actual file data 
1MB   File directory and names and a pointer to where the file contents is located
0 MB  Partition table

Type A
With a Type A device, you can copy 16GB of files to it and it will appear to have stored them all. If you look at the memory device using Windows Explorer, all the file names will be there and it will look fine. You will be able to access any files that are stored on the device up to the 2GB point. Any files stored after 2GB will be corrupt (probably all 0's or 1's).

Type B
These memory devices will appear to work until you put too many files on them (e.g. in the case above, if you put more than 2GB of files on it.) Once you exceed the true memory capacity, the next file that you write to it will actually start writing at 0MB which is where the file directory is located. This means that the file directory is now corrupt and you cannot access any files at all!

Be careful!

If you buy one of these fake UFDs or SD cards, they will appear to work fine and Windows will show them at their 'rated' capacity - for instance a 64GB UFD will appear in Windows to have a capacity of say 61.3GB, you may even give the seller positive feedback on eBay because they appear to work fine. However, these UFDs actually only contain about 2GB of real memory. When you start putting your files onto it, everything may appear to be fine - until you fill it up with more than 2GB and then it completely corrupts all the files on it! Bet you wish you hadn't paid £20 for it now!

The fake product is usually made from a poor quality or defective smaller flash memory chip (and probably a 2nd rate 'reject' memory chip obtained from the trash can at the back of the factory!), but the controller has been programmed to falsely report it's capacity as say 64GB to Windows.

Don't be caught by these cheats. Simply ask them to test the UFD using RMPrepUSB, FakeFlashTest or H2TESTW before you buy it. If they refuse then walk away from the deal! Explain to them that if the UFD passes H2TESTW they will get a lot more bids if they state this in their adverts.

Do you have a fake Kingston Flash Drive? One simple way to check, is that usually Kingston print text onto the metal USB connector which has the model number and capacity + other numbers. If your Kingston drive has no printing on the connector, it may well be a fake!

eBay, etc.

WARNING to all eBay buyers - Always check the seller's feedback - if anyone has given neutral or negative feedback because of 'corrupted' data, then it is likely that the product is counterfeit/fake. 
Always test the memory using RMPrepUSB - Quick Size Test or FakeFlashTest before you use it. It would be a shame if you used a 64GB SD card for all your photos on that 'once-in-a-lifetime' holiday to Africa, only to find out that all your photos have gone! Also, please ensure you give the seller negative feedback and report them to eBay for selling fake goods - if they knowingly continue to sell fake goods they are criminals and don't deserve good feedback! Also, get the eBay seller onto the eBay Fake Sellers list here.

Buying an SD card on eBay - If you are buying an SD/SDHC card from an eBay seller, check the full description very carefully. Some sellers are advertising a '16GB SD Class 10 SDHC card' and then in the description say 'these cards have been tested and may vary from 2GB to 32GB' and 'this is normal for cheap cards' and even 'the data you store will be compressed so don't worry if you can only store 2GB as really you can store more'. This is all a load of rubbish! These cards are 'fake capacity' cards and have been deliberately manufactured to deceive the buyer! eBay seem quite content to allow these sellers to sell their fake goods!

How to test a suspect UFD or SD card


If you have a USB Flash drive, try using ChipGenius. Often this will reveal the true size of the memory chips(s) fitted by the manufacturer. The screenshot below shows a fake 16GB USB Flash drive containing a  JS29F16G08AAMC1 memory chip which is a 16Gb  (Gigabit) or 2GB (GigaByte) memory chip. It therefore cannot possibly hold 16GB of data!

NEW! FakeFlashTest.exe - test your suspect 'fake' SD card or USB Flash drive in just a few minutes (rather than hours!) - read my blog.

Tip: For testing SD cards, you can buy a USB 3.0 card reader for £5 from Amazon - these really improve data transfer times (even if just using them on a USB 2.0 port). Cheap USB 2.0 card readers are notoriously slow!

Fill it with photos

A good practical test of a USB flash drive or SD card is to fill the drive up with .jpg photos (at least half-full). Then try looking at ALL the photos to see if they are all accessible and not corrupt. The thumbnail view in Windows Explorer will do this for you quite nicely! It can take a long time however. 

BE WARNED: If you already have photos/files on the memory device - copy them first (take a backup). Filling up the memory device with more files can cause the existing 'good' files to be corrupted and lost!


If you have bought a 'bargain' UFD, you can test it using the 'Gold Standard' test H2TESTW written by Harald Bogeholz for c't magazine. This test is very thorough but very slow because it tests all bytes of unused memory (even if it doesn't exist). 

The test utility is not included in the RMPrepUSB download but there is a link to the download on the RMPrepUSB help form - Just run H2TESTW.exe and select English as the language and the empty USB drive that you want to test. H2TESTW will fill up the empty, unused space on the UFD with large files but will not destroy any files that you already have on the UFD (but it you may lose all the files if the UFD is a fake one due to corruption!). The test can take 4-8 hours to test a good 16GB drive and considerably longer if it is faulty.

BE WARNED: If you already have photos/files on the memory device - copy them first (take a backup). Filling up the memory device with more files can cause the existing 'good' files to be corrupted and lost!

Quick Size Tests

A much quicker test is to use FakeFlashTest.exe or the Quick Size Test button in RMPrepUSB (both tests are very similar in action)

These tests destroy all data on the UFD and you will need to re-format the drive as FAT32 using RMPrepUSB after testing it, but a 16GB UFD can be  tested in just 6-10 minutes. 

Note that this is not a thorough test of all bits in the memory but it will certainly detect a 'fake capacity' memory product.

If it fails RMPrepUSB or FakeFlashTest, then it will also fail H2TESTW, so you might as well use RMPrepUSB to test it first as it will be much, much quicker! 

Bought on eBay - 32GB SD Class 10 card that is actually only 4GB and wasn't even Class 4! (click to enlarge)

See the bottom of this article for a typical result when testing a 'fake' flash memory drive.

If a Size Test passes, then (if you have the time) you should reformat it and then test it twice with H2TESTW just to make sure the memory is all good quality (if you have the time!). 

If it fails, the test will tell you the approximate true size of memory present (though the memory may be faulty/unreliable). 


I do not advise that you attempt to re-format or repair the device. Even if you get it for free - I suggest you throw it away or at least indelibly mark/scratch/chip it in some way so that you do not mistake it for a 'good' device!

To re-format it, you could set the SIZE box in RMPrepUSB with the reduced size and then reformat it as FAT32 to use what little memory is actually present - but don't use it for anything important as quite often that memory is faulty or will develop a fault at a later date! 

If you have a fake UFD, you cannot easily 'repair' them and even if you reformat them to their true (reduced) capacity using RMPrepUSB, the memory is probably of such poor quality (reject chips sold off by the factory as faulty) that it will sooner or later cause corruption of your most important files. You may not even realise your files are corrupt for months and may have lost the original files by the time you find out!

To reprogram a fake flash memory drive, you will need to find the manufacturer's tool to re-program it with the true capacity - for an example on how to do this see Tutorial #39.

For more details about fake UFDs, see SOSFakeFlash website here.

As far as I know, there are no 'repair' or reprogramming tools available for SD cards.

Problems accessing the device?

If you have a USB Flash Drive that does not seem to work with Windows and causes the computer to slow up or stop responding whenever you try to use it or access it - please read the Tutorial #23 here for instructions on how to fix it. 

If your USB Flash drive does not seem to format using RMPrepUSB, check that Windows has assigned it a drive letter. If not use Drive Manager to add a drive letter to the drive.  The easiest way to access the disk management console is go to Start-Run and enter "diskmgmt.msc" right-click on the USB drive area and choose 'Change drive letter and paths...' - then add a drive letter.

Test Results

Here is a typical 'fake' flash drive bought from China off eBay. It was sold to me as a 16GB Flash drive and has 16GB printed on it.
However, it is actually a 2GB Flash chip mapped 8 times into a 16GB address space - writes past 2GB don't actually store the data but just report back 'OK' - hence writes and reads from 16GB to 2GB are very quick!

COMMAND LINE: drive=2 quicktest 

RMPARTUSB v2.1.631 (c)2011 RM Education plc [SSi]

Accessing Drive 2 - "USB 2.0" (17,179,869,184 bytes)

Writing marker blocks to drive 2

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Reading back marker blocks...
Error at Block 33554431 - found Block -1 instead!
Error at Block 33538047 - found Block -1 instead!
Error at Block 33521663 - found Block -1 instead!
Error at Block 33505279 - found Block -1 instead!
Error at Block 33488895 - found Block -1 instead!
Error at Block 33472511 - found Block -1 instead!
Error at Block 33456127 - found Block -1 instead!
Error at Block 33439743 - found Block -1 instead!
Error at Block 33423359 - found Block -1 instead!
Error at Block 33406975 - found Block -1 instead!
Error at Block 33390591 - found Block -1 instead!
Error at Block 33374207 - found Block -1 instead!
Error at Block 33357823 - found Block -1 instead!
Error at Block 33341439 - found Block -1 instead!

(lots more errors here!)

Error at Block 4227071 - found Block -1 instead!
Error at Block 4210687 - found Block -1 instead!
Error at Block 4194303 - found Block -1 instead!
Error at Block 4177919 - found Block -1 instead!
Error at Block 4161535 - found Block -1 instead!
Error at Block 4145151 - found Block -1 instead!
Error at Block 4128767 - found Block -1 instead!
90% complete - 0 min 1 sec remaining
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100% complete - 0 min 1 sec remaining
Memory tested in blocks of 16384 sectors.

BAD MEMORY from sector 4128767 (2016.0Mib) to sector 33554431 (16384.0Mib)
WARNING: no memory detected at one or more locations.
Recommended maximum usable partition size: 2007Mib (Sector=4112383)

Test took 50 seconds.
Finished testing - now wiping MBR...
MBR and partition table erased.

*** FAILED ***


Recommended maximum usable partition size: 2007Mib (Sector=4112383)


Keywords: USB, corrupt flash drive, thumb drive, not responding, slow, freeze, hang, stop, access, bad, cheap, fake, pen drive, size, capacity, china, hong kong, taiwan
Selection File type icon File name Description Size Revision Time User

Release version (USB only) - quick size test for flash memory devices. Much faster than H2TESTW. 42k v. 1 29 Sep 2014, 11:08 Steve Si

NEW IMPROVED VERSION! With 'List all drives' checkbox for SD card readers as well as USB drives (CAUTION: Do not select your hard disk drive by mistake!). 43k v. 1 1 Jan 2015, 02:04 Steve Si
Selection File type icon File name Description Size Revision Time User
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