When a USB drive needs replacement, not repair

A USB drive or SD card that suddenly becomes unreadable can look like a simple software problem. Sometimes a file system check or format helps, but neither can fix failing flash memory or make a counterfeit drive hold the capacity printed on its label.

Before deciding, protect any files you still need and check whether the drive can reliably store and read data. The Fake USB & SD Check can test a drive's real capacity, but it writes data to the drive, so prepare it carefully.

Check the drive safely

1. Copy any files you can still open to another device. If the drive contains the only copy of important files and is repeatedly disconnecting or making errors, stop using it and consider professional data recovery before running a test.
2. Use an empty USB drive or SD card, or make sure everything on it is backed up. The check writes test data across the drive and reads it back. Do not run it on a drive containing files you need to keep.
3. Open the Fake USB & SD Check in Chrome or Edge on a computer. Other browsers may provide a reduced version or no access to the drive test.
4. Connect the drive directly to the computer if possible, rather than through a hub. Select the drive in the tool and run the capacity check. Let it finish without unplugging the drive or closing the browser tab.
5. Compare the amount of data verified with the capacity printed on the drive or card. If the test reports errors or cannot finish, back up anything still readable and check the drive again in a different port or card reader before you decide.

What the result means

The verified capacity is much smaller than the label

The drive may be counterfeit or may have a failing memory chip. A drive can report a large capacity to the computer even when it has much less real storage. Formatting it will not add capacity. If it is new, return it to the seller. If it is old, replace it rather than trusting it with files.

The test finds read-back errors

Data written to part of the drive did not come back unchanged. That can point to failing memory, a damaged controller, or a connection problem. Try one other port or reader, then test it on another computer if practical. Repeated errors across connections are a strong reason to stop using the drive.

The drive disconnects or the check stops

A loose port, card reader, adapter, or cable can interrupt a test, so rule out the connection first. If the same drive disconnects on more than one device, do not rely on it for storage. A format will not fix an unstable connection inside the drive.

The capacity check completes, but files still will not open

The result only checks whether data can be written and read during this test. It does not prove that the file system is healthy, that every file is intact, or that the drive will keep working. The problem may be limited to file-system damage, which an operating system check may repair.

What to try before replacing it

1. Check the connection and lock switch. Try a different USB port or card reader. Some SD adapters have a small lock tab on the side. Move it to the unlocked position and try writing again.
2. Copy readable files first. Do not use a repair tool or format the drive before saving what you can. If files matter and copying causes repeated errors, stop. Continued attempts can make recovery harder.
3. Check the file system. In Windows 11, open File Explorer, select This PC, right-click the drive, choose Properties, open Tools, then choose Check. On macOS, open Applications › Utilities › Disk Utility, select the volume, then choose First Aid. These checks can address file-system problems, not failing memory.
4. Try another computer. If the drive works there, check the original computer's port, reader, or permissions. If the same errors follow the drive, the drive itself is more likely to be at fault.
5. Format only when you have a backup. Formatting erases the drive and creates a new file system. In Windows 11, use File Explorer, right-click the drive, and choose Format. On macOS, use Applications › Utilities › Disk Utility, select the drive, and choose Erase. If errors return after formatting, replace the drive.

When the drive needs replacement

Replace a USB drive or SD card if it repeatedly reports less usable capacity than its label, produces read-back errors on more than one device, or disconnects despite a reliable port or reader. A drive that becomes read-only across multiple devices may also be protecting itself because its controller or memory is failing. Do not use it as the only copy of anything important.

Most USB flash drives and memory cards are not practical to repair. If the drive is under warranty, ask the seller or manufacturer about a replacement, but do not send it away if you still need the data unless you understand the data and privacy terms. For important files on a failing drive, a data-recovery service may be able to retrieve them. Recovery is different from repairing the drive for safe future use.

What a capacity check cannot tell you

A capacity test can catch a drive that claims more storage than it can really hold. It is not a full health report and cannot predict how long the drive will last. A drive may pass one test and fail later, so keep a second copy of important files even when the test completes without errors.

The check runs in your browser, and the files on your drive stay on your device.