How to test a microSD card for rollover errors

Your microSD card may show the advertised size but still fail when you fill it. A card with a false capacity can start overwriting older files after it reaches its real limit, so photos and videos may appear saved but later turn out damaged or missing.

Use the Fake USB & SD Check to write test data to the card and read it back. The check needs a computer and a microSD card reader, and it can overwrite existing data. Back up anything you want to keep before you begin.

Check the card for rollover errors

1. Copy every file you need from the microSD card to another location. Do not run a full-capacity test on a card that contains the only copy of important files.
2. Put the card in a computer using a card reader. Open the Fake USB & SD Check in Chrome or Edge on a computer. The tool has reduced or no support in other browsers.
3. Choose the microSD card, not your computer's internal drive or another removable drive. Check the drive name and reported size before you continue.
4. Start the capacity check and allow it to write test data across the card. Keep the card connected and the browser tab open while it runs. A large card can take a while to fill and verify.
5. Wait for the read-back check to finish, then compare the amount verified with the card's usable capacity. If the test fails, repeat it with a different reader before deciding whether the card itself is faulty.

A full capacity test writes data to the card. Do not remove it, close the browser, or turn off the computer during the check. If the card disconnects or the browser stops responding, avoid relying on the card until you have checked its files and tested it again.

What the result means

The full capacity is written and read back successfully

The card stored and returned the tested data without a capacity error in this run. That is a good sign, but it does not prove the card will never fail or confirm that its brand and speed rating are genuine. Keep a separate backup of files you cannot replace.

The test fails near a smaller, repeatable capacity

If a card sold as 128 GB repeatedly fails after about the same smaller amount, its real storage may be less than advertised. A counterfeit controller can report a larger size than the memory actually holds. When the real memory fills, new data can overwrite earlier data, which is the rollover problem.

The test fails at changing points or the card disconnects

An inconsistent failure can point to damaged flash memory, a loose connection, or a card reader problem. Try another reader and USB port, then run the check again. If errors continue, treat the card as unreliable even if some files still open.

The card does not appear in the browser's drive list

The browser may not support the required file access, or the computer may not be detecting the card reader. Use Chrome or Edge on a computer, reconnect the reader, and check whether the card appears in File Explorer on Windows or Finder on macOS.

How to fix a failed check

1. Back up readable files. Copy anything you can still open to another drive before trying more tests. Do not save new photos or documents to a card that has failed a capacity check.
2. Check the card adapter. If the microSD card is inside a full-size SD adapter, make sure the adapter's lock tab is not set to lock. The tab does not prove the card is healthy, but it can prevent writing.
3. Reconnect the card. Remove and reinsert it, then try a different USB port or reader. Check the card and reader contacts for dirt or damage. Do not scrape or wet the contacts.
4. Test with another reader. A faulty reader or adapter can cause write errors that look like a bad card. If the card passes with a second reader, replace the first reader or adapter and check the card again before using it for important files.
5. Retest only after securing your files. Use a backed-up card and let the test finish without interruption. If it fails at a similar capacity in more than one reader, do not use it to store important data.

When the card needs replacing

A repeatable rollover failure is not something formatting can repair. Formatting changes how the card organizes files, but it cannot add missing physical memory or make defective flash storage dependable. If the card is new, save the test result and request a refund or replacement from the seller. If it is old and the test fails across multiple readers, replace it and restore your files from a backup.

Why rollover can hide until the card fills up

A card can look normal when it is empty because its controller reports the capacity the device expects to see. The problem appears only after enough data has been written to reach the actual storage limit. That is why copying a few photos or checking the number shown in a file manager cannot confirm the card's real capacity. A write-and-read check tests storage across the card instead of trusting the label or reported size.

The capacity check runs in your browser, and the test data stays on the card and your device.