Why counterfeit storage works until the drive fills up

A counterfeit USB drive or memory card can appear to work for days. It saves files, shows plenty of free space, and may open everything you put on it at first. The trouble often starts only after you store more data than the flash memory can really hold.

Here is why that happens, what damaged files can tell you, and how to check a drive's usable capacity. The Fake USB & SD Check fills a drive with test data and reads it back, so use it only after backing up anything you need.

Check the drive's real capacity

1. Copy anything important from the USB drive or SD card to a different, trusted device. The test writes data to the drive, so do not run it on storage holding the only copy of your files.
2. Connect the drive to a computer. The Fake USB & SD Check works in Chrome and Edge on a computer. Other browsers may offer a reduced version or no access to the drive.
3. Open the Fake USB & SD Check, choose the drive when prompted, and follow the browser's instructions to grant access.
4. Let the test write data and read it back. Avoid unplugging the drive or letting the computer sleep during the check.
5. Review the verified capacity and any read-back errors. A mismatch means some data could not be stored and retrieved reliably across the space the drive claimed to have.

Run this check on an empty drive or one whose contents are backed up. If the drive contains files you cannot replace, do not fill it just to confirm a suspicion.

What the result means

The test finds a much smaller usable capacity

The drive cannot reliably store everything it claims it can. A counterfeit controller may report, for example, 256 GB even though the device has only 16 GB of flash memory. Once writes pass the real limit, the controller may direct new data into flash already holding older data. The drive can still show the advertised capacity in the operating system, while older files become corrupted or contain newer data.

Stop using it for anything important. Formatting it does not add memory or make the reported capacity true.

The test reports read-back errors

The data written to part of the drive did not come back correctly. Counterfeit capacity is one possible cause, but worn or faulty flash memory, a bad card reader, or an unstable USB connection can also cause errors. Test again only after backing up the drive, and try another port or reader to rule out a connection problem.

The test verifies the expected capacity

The drive passed this write-and-read check at the tested capacity. That is useful evidence, but it does not guarantee the drive will keep working indefinitely or prove its brand and history are genuine. Keep another copy of important files.

The computer shows less space than the label

A modest difference can be normal because manufacturers and operating systems count storage units differently. A drive sold as 1 TB may show roughly 931 GiB in a computer. That difference alone does not mean the drive is counterfeit. A much larger gap, or files failing after the real flash capacity is exceeded, is more concerning.

Some files appear in the folder but will not open

A file listing does not prove its contents are intact. The folder information may still say a file exists even when some of its data has been overwritten. Stop saving new files to the drive. If the files matter, see what to do first when recovering data from a fake drive.

What to do if the drive fails

1. Stop writing to it. New files and repeated tests can overwrite data that might otherwise still be readable. Do not format the drive or run repair tools before copying anything you can still open.
2. Copy readable files to another device. Copy, rather than move, the files. Open the copies from the other device to check that they work. Do not treat the suspect drive as the only safe location for anything.
3. Check the connection once. If the drive disconnected or the test stopped, reconnect it directly to another USB port or use a different card reader. Avoid hubs while checking, since a poor connection can interrupt writes.
4. Test only after making a backup. Use the Fake USB & SD Check on a drive with no needed files. If it repeatedly verifies far less space than the label claims, or read-back errors return, consider the drive unreliable.
5. Return or replace it. Save the test result and purchase details if you plan to request a refund. Do not keep using a drive that fails capacity verification for backups, documents, or other important files.

When the drive itself is faulty

A drive that fails in the same way on more than one computer and reader is less likely to have a simple connection problem. Repeated capacity mismatches point to false capacity reporting; read-back errors at a plausible capacity can point to failing flash memory. Either way, the drive is not dependable for storing files.

If the data matters, stop testing and seek data recovery help before attempting more writes. If the drive is new, return it or ask the seller for a replacement. For a memory card supplied with a camera or other device, replace it with a card from a trusted seller and verify it before relying on it.

Why the failure can wait until the drive is full

The computer trusts the capacity reported by the drive's controller. With counterfeit storage, that number can be much higher than the amount of physical flash memory inside. Early writes fit, so the first few files may work normally. Once the real memory is used, later writes may overlap earlier data, be discarded, or fail during read-back, depending on the controller.

This is why a quick check such as saving one photo or opening an empty folder proves little. A capacity check has to write data across the space the device claims to have, then read it back. The check can find a capacity mismatch, but it cannot restore files that have already been overwritten.