The pendrive claims 512 GB. Windows believes it, formats it, and shows it. Then files copied past about 16 GB quietly destroy each other. This is the fake capacity fraud - the drive is lying about its size, and here is how to prove it and what to do next.
A fake capacity drive contains a small, cheap memory chip - 8, 16 or 32 GB - with its controller reprogrammed to report a much larger size to the computer. Everything looks normal until your copied data passes the real capacity. From that point the drive wraps around and starts overwriting the files you copied first. No error appears while it happens. That silent corruption is what makes this fraud worse than a simple dead drive.
Every storage device tells the computer its capacity; the computer trusts that answer completely. Fake drives are programmed to give a false answer. The operating system then formats the full fake size and keeps a file index for all of it - but the physical memory ends much earlier. Writes beyond the end loop back to the beginning of the chip. So the newest files overwrite the oldest, and the index still claims everything is present until you actually open the files.
One symptom alone proves nothing. The pattern - fine when nearly empty, corrupt when full - is the signature.
H2testw is a long-standing free test tool built for exactly this fraud. It fills the entire reported capacity with numbered test data, then reads it all back and verifies every byte. On a genuine drive it finishes with no errors. On a fake, it reports the true usable size and shows errors starting exactly where the real memory ends. Run it on an empty drive (it writes everywhere), and accept that a big fake drive takes a long time to fill - the wait is the proof.
Be clear-eyed: formatting cannot make the missing capacity exist. Your options are: return the drive and report the seller if any route exists; or, if you keep it, treat it as only its real size and never copy beyond that - possible, but risky, because the wrap-around corruption gives no warning when you misjudge. For anything important, the correct option is to stop using it. A drive that lies about its size has told you everything about its quality.
The video covers the wider family of pendrive format failures - watch it to see how these drives present in Windows.
▶️ Watch Full VideoWindows displays the capacity the drive's controller reports - it has no way to independently measure the memory. The controller is exactly the part the fraud reprograms. Only a fill-and-verify test like H2testw measures the truth.
You can partition or format only the real capacity if you know it exactly, and some technicians reprogram controllers with vendor tools. For a normal user the honest answer is that the drive stays unreliable - one misjudged copy corrupts silently. Return it or retire it.
No. Plenty of honest budget drives exist; they are simply small, slow, or both. The fraud sign is capacity wildly out of line with price. A quick H2testw run on any new drive separates honest cheap from fake in one test.