Memory card loses data after copying: why it happens

You copy photos or videos to a memory card, see them appear, then find that some are missing or unreadable later. A quick copy can look successful even when the card has not safely stored every file.

Common causes include a counterfeit card, a failing card, or removing it before pending writes finish. Here is how to protect what is still readable and check the card with the Fake USB & SD Check.

Check the card safely

1. Back up any readable files to another device first. The Fake USB & SD Check writes data to the card and reads it back, so do not run it on a card that holds the only copy of important files.
2. Use an empty card or one whose contents you have safely copied elsewhere. Connect it to a computer with a reliable card reader.
3. Open the tool in Chrome or Edge on a computer. Other browsers may offer a reduced version or no access to this check.
4. Follow the tool's on-screen request to select the card, then let the write and read-back check finish. Do not remove the card or close the browser while it is working.
5. Check whether the test reports that all written data could be read back. If it finds a mismatch or cannot finish, stop using the card for files you need to keep.

A full-card test takes longer than copying one small folder because it checks data across the available capacity. A short test cannot prove that every part of a card is reliable.

What the result means

The test finds less usable space than the card claims

The card may be counterfeit or faulty. Some fake cards report a large capacity to the computer but have much less physical storage. When you write beyond the real capacity, new data can overwrite earlier files or become unreadable. Read more about why counterfeit storage can appear to work until it fills up.

The test finds read-back errors

The card did not return the same data that was written. That can point to failing flash storage, a damaged card, or a poor connection through the reader or adapter. Try a different reader once, but do not trust the card with important data unless it passes a complete check afterward.

The test passes, but files still disappear in your device

The card may be fine in the test, while the camera, phone, adapter, or file system has another problem. Check that the device supports the card type and capacity, and test the card in a different reader. A browser test cannot confirm that a camera can sustain the speed needed for a particular recording mode.

The tool cannot access the card

The browser may not support the needed access, or the card reader may not be available to the computer. Try Chrome or Edge on a computer and reconnect the reader. If the card is not visible there either, check the reader, adapter, and card contacts.

How to prevent more data loss

1. Stop writing to the card. New photos and files can overwrite data you may still be able to recover. Copy readable files to a separate drive before troubleshooting further.
2. Wait for transfers to finish. A copy window can disappear while data is still being written from a system or device cache. Wait for the device's activity light to stop before removing the card.
3. Eject the card before unplugging it. In Windows 11, use the taskbar's Safely Remove Hardware and Eject Media menu and choose the card reader. On macOS, use Finder and click the eject icon beside the card before disconnecting it.
4. Check the adapter and lock switch. If you use a full-size SD adapter, make sure its small lock tab is not in the locked position. Try another adapter or reader if the card disconnects or becomes read-only.
5. Check compatibility in the device manual. A camera or phone may not support the card's format or capacity. If the device asks to format the card, do not accept until you have copied any files you need.
6. Retest with a different reader. If errors only happen through one reader, replace that reader. If the same card fails in more than one reader, replace the card rather than relying on it.

When the card needs replacement

If a full write and read-back check reports errors, or files keep disappearing in multiple devices, retire the card. Formatting may make it appear usable again, but it does not repair failing memory or make counterfeit capacity real. If the files matter and are not backed up, avoid formatting or running more tests. A data recovery service may be able to help, but recovery is not guaranteed.

For a card that is still under warranty, keep the purchase details and test result, then contact the seller or manufacturer. Replace a card that fails repeatedly, even if it sometimes works after reconnecting.

Why a quick copy can look successful

A file appearing in a folder does not always mean every byte has reached stable storage. Computers can temporarily hold writes in memory, and a card may report completion before a delayed fault becomes visible. If you remove the card too soon, the last files may be incomplete.

A counterfeit card can also accept data at first. When its real storage fills, later writes may overwrite earlier data or return corrupted contents. That is why a small copy is not a capacity test. A read-back check compares stored data with what was written, as explained in how read-back tests uncover storage errors.

Keep at least one separate copy of important photos and videos, even when a memory card passes a test.