How to test an SD card for counterfeit storage

Your SD card says 256 GB, but files disappear after you copy them, or the card seems to fill up far too soon. A counterfeit card can report more space than its memory can actually store. When it reaches that false capacity, new data may overwrite older files without warning.

You can check the card by writing test data and reading it back. The Fake USB & SD Check does this in your browser. Use it only after backing up anything you need, because the test fills the selected storage.

Test the SD card safely

1. Copy every file you want to keep to a different drive or device, then check that the backup opens. Do not rely on a second folder on the same SD card as a backup.
2. Put the card in a reader connected to a computer. Open the Fake USB & SD Check in Chrome or Edge. This tool's full drive check is available in these browsers on a computer, not on a phone.
3. Follow the browser's file-access prompt and select the SD card or a location on it, as requested by the tool. Make sure you have selected the card you intend to test, not another drive.
4. Start the check and let it write data to the card and read that data back. Keep the card connected, and do not remove it or close the browser while the test is running. A large or slow card can take a while.
5. Compare the verified amount with the card's advertised capacity. If the test reports errors or cannot reach the advertised size, do not store important files on the card.

The check needs room to write test data. A card containing files may not have enough free space for a full-capacity test, and counterfeit storage can damage data when writes exceed its real memory. Back up the card, then use an empty card for the check whenever possible.

What the result means

The test writes and reads back the advertised capacity

This is evidence that the card can store data across the tested space. It does not guarantee the card's long-term reliability, write speed, or suitability for a camera's recording demands. Keep a separate backup of important photos and videos.

The test fails before reaching the labeled capacity

The card may be counterfeit, damaged, or unable to hold the space it reports. Some fake cards are programmed to claim a large capacity even though they have much less memory. Once writes pass the real limit, data can wrap around and replace files written earlier. Learn more about this behavior in why counterfeit storage works until the drive fills up.

The test reports read-back errors

The data written to part of the card did not come back as expected. A counterfeit card is one possible cause, but a failing card, loose connection, or faulty reader can also cause errors. Do not trust the card with files you cannot replace. Try another reader once, then test again before deciding whether the card itself is at fault.

The card is not available to the browser

This does not prove the card is fake. The browser may not have access, the card may not be mounted, or the reader may not be working. Check that the computer can see the card before running the capacity check.

The computer shows less space than the label

A small difference is normal because card makers use decimal units, while operating systems may display capacity using binary units. For example, a card labeled 128 GB may appear close to 119 GiB, sometimes shown as GB by the operating system. A modest display difference is not the same as a test failing far below the card's claimed capacity.

How to fix a test that will not run

1. Use a computer with Chrome or Edge. The full Fake USB & SD Check works in these browsers on a computer. If you are trying on a phone or in another browser, switch to a supported setup before drawing conclusions about the card.
2. Check that the card is connected and visible. On Windows 11, open File Explorer › This PC and look for the card. On macOS, open Finder and check under Locations. If it is missing there too, the problem may be the reader, adapter, or card connection.
3. Reinsert the card and check the adapter. Remove and reseat the card. If you use a full-size SD adapter, check that its small lock switch is not in the locked position. The lock switch prevents writing, so the test cannot fill the card while it is locked.
4. Try another port or reader. Connect the reader directly to a different USB port rather than through a hub, if possible. Then try the card in another reader. If it works there, the first reader or connection may be the cause.
5. Allow file access when the browser asks. The test needs permission to work with the selected storage. If you denied access, reopen the tool and select the card again when prompted. Do not grant access to a different drive by mistake.
6. Stop using a card that fails verification. Do not format it and assume the capacity is fixed. Formatting changes the file system, not the card's actual memory. If the card is new, save the result and contact the seller for a return or refund.

When the card is counterfeit or faulty

A failed check on one reader is a reason to investigate, not final proof. Repeat the test with a known-good reader if available, using an empty card and the same supported browser. If it fails in the same way, treat the card as unreliable. Do not use it for camera footage, travel photos, backups, or other files you need to keep.

If you bought the card recently, contact the seller or manufacturer and include the label, purchase details, and test result. Keep copies of any evidence outside the card. The guide to preparing evidence for a counterfeit drive dispute can help you document the problem.

Why a quick copy test can miss a fake card

A counterfeit card may appear to work when you first copy a few photos because those files fit within its real memory. The false capacity becomes apparent only when the card is filled and the data is read back. That is why copying a small file to the card, or checking the free-space number shown by your computer, cannot confirm its true capacity.

Keep the card connected until the test finishes, then safely eject it before removing it from the reader.