How to validate flash storage bought online

A USB drive or SD card can look normal, show the advertised size, and still hold far less data than the label claims. Counterfeit storage may even seem to work until you save enough files to reach its real capacity.

Test the full capacity before trusting the drive with photos, documents, or backups. The Fake USB & SD Check writes test data to the selected drive and reads it back to check whether the reported capacity is real.

Test the drive's real capacity

1. Back up anything you need from the USB drive or SD card. The check writes data across the storage, so treat the drive as empty before you start. See how to back up data before testing a flash drive.
2. On a computer, open the Fake USB & SD Check in Chrome or Edge. The tool works in these browsers on a computer. Other browsers may offer a reduced version or none.
3. Connect just the drive you want to check, then follow the prompts to select it. Take care to choose the removable drive, not another disk or folder.
4. Run the capacity check and let it finish writing and reading test data. Do not unplug the drive, close the browser tab, or let the computer go to sleep while it is working.
5. Keep a record of the result. If it fails, save a screenshot and keep the marketplace listing, order details, packaging, and any photos of the label.

A full-capacity check can take a while, especially on a large or slow card. Do not stop it just because the drive appears in your computer with the expected size. That size can come from what the drive reports, not what it can reliably store.

What the result means

The full test passes

The tested storage area accepted data and returned it correctly during the check. That is a useful sign that the drive can hold the capacity it reports. It does not prove the brand is genuine, predict how long the drive will last, or confirm its advertised speed. A counterfeit product could still pass a capacity check if its usable size matches the reported size.

The test finds less usable space than the label promises

The drive may have counterfeit capacity, or the selected storage may be limited by its partition or file system. A fake drive can report a large size while its flash memory holds much less. When writing reaches the real limit, new data may overwrite earlier data or fail to read back correctly. Do not trust it with important files.

The test reports read or write errors

The drive, card reader, connection, or file system may be causing the problem. A single error does not identify which part is at fault, so check the connection and repeat the test with the drive empty. If the same errors return on another port or reader, consider the storage unreliable.

The computer shows less space than the package lists

A smaller displayed number does not by itself mean the drive is fake. Manufacturers usually label storage in decimal units: 1 TB means 1,000,000,000,000 bytes. Some operating systems display that same capacity using binary units, so a 1 TB drive may appear as about 931 GiB, before formatting and system information take up space. Look for a major shortfall, not a small difference in how units are displayed.

How to fix it

1. Check that you selected the right drive. Disconnect other removable drives and try again. A wrong selection can produce a misleading result or put test data somewhere you did not intend.
2. Retry with a direct connection. Connect the drive to another USB port or use a different card reader. Avoid a hub for the retest, since an unreliable connection can interrupt a long write or read.
3. Use a supported browser and computer. Run the check in Chrome or Edge on a computer. If the tool cannot access the selected storage, try the other supported browser and follow its prompts for file access.
4. Repeat the check on an empty drive. Back up any files first, then run the test again. A repeat failure on a separate port or reader makes a drive fault or false capacity more likely.
5. Contact the marketplace seller if it still fails. Send the test result and clear evidence of the advertised capacity. Ask for a refund or replacement through the marketplace's normal process, and avoid formatting or using the drive for important files while the claim is open.

When the drive is not safe to use

If a second test reports the same capacity shortfall or read-back errors, treat the device as faulty or misrepresented. Do not try to fix a capacity failure by formatting the drive. Formatting can change how the space is organized, but it cannot add flash memory or make a false capacity claim true.

If you already copied files to a drive that fails, stop writing to it. Save any readable files elsewhere and do not rely on the drive as the only copy. For marketplace evidence, document the test and the item exactly as received. The guide to preparing evidence for a counterfeit drive dispute explains what to keep.

What a capacity check cannot prove

This check verifies the storage you selected by writing data and reading it back. It does not authenticate the manufacturer's logo, prove that the seller's listing is honest, or measure sustained transfer speed. For speed, use a separate speed test, and compare results under the same connection and reader conditions.

The test runs in your browser, and the files used for the check stay on your device.