Test A USB Flash Drive For Errors Or Fake Size

H2testw is a simple way to test for fake or faulty USB (and hard) drives or memory cards. Seen a large capacity USB flash drive at a price that seems just too good to be true? If it isn’t from a reputable retailer, it probably is…

Unscrupulous sellers (especially on auction sites) may offer cheap flash drives that are faulty or have a fake size. Fake size – e.g. a flash drive sold as 32GB that is really only 4GB – the capacity is ‘remapped’ to display as 32GB in Windows.

Faulty – e.g. faulty drives (lots of bad sectors, rejected by the manufacturer) are low level formatted to hide the bad sectors from view. Such drives are likely to deteriorate further, causing more errors – which is why they were rejected in the first place. It can also be useful to test your older flash drives for errors before relying on them for backup.

How To Test – H2testw is a free portable program to check a USB flash drive for errors or a fake size – it works on Windows XP, Vista and Windows 7 (probably W8 too). It’s simple to use and can also test memory cards and even internal/external hard drives.

H2testw works by filling the chosen target drive with test data (random files up to 1GB in size) and then reading it back and verifying it. Although it does not overwrite or erase any existing data, if the drive is already defective the program might (as a side effect of writing more data to it) damage existing files.

It is therefore highly recommended to test only an empty drive – copy any data off first then quick format it or delete any contents before testing.

Using H2testw – The program homepage is in German but there is a Google Translate version in English here. (The program itself has an English interface option and a Readme in English). Click the Download button to visit the Download page and select ‘Download directly from Heise.de’ to download the program in a zip file.

Extract the zip file and in the h2testw_1.4 folder you will see the program itself and a Readme file (in English or German).

  • Run the program and change the language to English:


  • Click ‘Select target’ and browse to/select the flash drive (or other device) you wish to test.
  • For best results, choose ‘All available space’ in the Data Volume section
  • Press ‘Write + Verify’ to begin testing
  • A progress window shows the time remaining which will depend on the size of the drive (and whether it has errors) – a genuine 4GB drive took 10 minutes in my tests:


  • When the test completes, the results are displayed – ideally it should say ‘Test finished without errors’:


If the results show that ‘The media is likely to be defective’ and there is a substantial amount of data lost or bytes corrupted/other errors then the drive is probably faulty – or a fake if the number of GB that are OK is far less than the supposed capacity.

You can Copy the test results To Clipboard and paste into an email/document – useful if you need to complain to the seller or claim on warranty. H2testw leaves its test files (1.h2w etc) on the drive after it finishes – you can delete these.

H2testw Errors – There may be other possible causes for data corruption. In case of error you should therefore repeat the test and format the drive immediately before testing (backup any data first). Also try again without a USB extension lead, using a different port (USB ports at the back of a PC are usually better than those at the front) or, for external hard drives, try another cable if possible.

See the Readme file (in the program folder) for further info on error messages and typical errors.


H2testw is a simple way to test for fake or faulty drives – USB drives, memory cards and hard drives. It is particularly useful to run it on a brand new drive to test that it is working fine and has the correct capacity.