Back up data before testing a flash drive

A flash drive capacity test writes data to the drive and reads it back to check how much storage really works. That can expose a counterfeit drive, but it can also overwrite or corrupt files, especially when a drive claims more capacity than it has.

Back up everything you need before testing. Use a separate storage device or a verified cloud copy, and keep the original files until you have checked the backup. The Fake USB & SD Check can help check a drive's real capacity after your files are safe.

Back up the drive before testing

1. Open the Fake USB & SD Check to confirm you have the right tool, but do not start the capacity test yet. It works in Chrome and Edge on a computer. Other browsers may provide a reduced version or none.
2. Choose a separate destination. Connect another drive or choose a cloud location with enough free space for everything on the USB drive. Do not back up to the drive you plan to test, or to another partition on that same drive.
3. Copy, do not move. In File Explorer on Windows or Finder on macOS, copy the files and folders to the backup destination. Include all folders you recognize, and check the destination before deleting or changing anything on the original.
4. Check the copy. Open several files from the backup, including files from different folders. Compare the folder and file counts if practical, and confirm that the backup destination shows the copied files rather than shortcuts or placeholders.
5. Only then run the test. In the tool, select the USB drive or SD card and follow the browser's access prompt. Expect the test to write data to the selected drive. Do not remove it while the test is running.

If the drive contains work, family photos, or anything you cannot replace, keep a second backup as well. A copy is useful only if you can open it and it is stored somewhere other than the drive being tested.

What the backup and test results mean

The backup copy opens correctly

This is a good sign that you have a usable copy of the files you checked. It does not prove that every file copied successfully, so check important folders and look for copy errors before testing. Keep the originals until the capacity test is finished and you have confirmed your backup is still available.

The copy reports errors or some files will not open

Do not start the capacity test. The source drive may already have damaged files, or the cable, card reader, port, or destination may have interrupted the copy. Retry the files that failed and check them on another computer if you can. If the files matter, avoid further writes and seek recovery help before experimenting.

The capacity test reads back the written data

The result supports that the tested storage area can be written to and read back. It does not prove that every existing file is intact, that the drive will last, or that it is safe as the only copy of important data. Keep your backup even after a successful test.

The test finds less usable capacity or read-back errors

Stop using the drive for important files. A mismatch can indicate counterfeit capacity, damaged storage, or a connection problem. Do not keep copying valuable data to it while troubleshooting. If files were already damaged during a test, see Fake drive data recovery: what to do first before writing anything else.

If you cannot make a reliable backup

1. Check the destination space. Make sure it has room for the files, then try another destination if it does not. A test drive is not a backup location.
2. Copy in smaller groups. If one large copy stops, copy a few folders at a time and note which files fail. Do not delete the originals to save space until the copies have been checked.
3. Reconnect the drive. If copying fails repeatedly, try a different USB port or card reader and copy the files again. Avoid disconnecting a drive while files are being transferred.
4. Stop if the drive keeps disconnecting. Repeated errors or a drive that disappears during copying may point to a failing drive or connection. For irreplaceable data, contact a recovery professional before running a capacity test or trying repair tools.

Make room for a safe test

The Fake USB & SD Check fills a USB drive or SD card with test data and reads it back to find its real size. That is why backing up first matters: on a counterfeit drive, writing past its actual capacity can damage data that seemed to copy successfully earlier. The tool is not a backup utility, and a capacity result cannot restore files.

If you have verified your copies, you can use an empty spare drive for the test. Do not assume that files on the test drive will remain untouched or that the drive will contain its original contents afterward. Keep your backup until you have decided whether to keep, return, or replace the drive.