What causes it
Every card has a file system: an index that records which files exist and where each one sits. When a camera or computer can’t read that index, it has no way to show you the files, so it offers the one thing it knows how to do, which is to wipe the index and start a new one.
The message is about the index, not the photos. In most cases the pictures and video are still on the card in the places they were written.
The usual ways the index gets damaged:
- The card was pulled out, or the camera was switched off, while it was still writing.
- The battery died in the middle of a shot or a recording.
- The card has been moved between several cameras, phones and computers, each of which treats it a little differently.
- The card reader or the cable glitched during a transfer.
- The card itself is wearing out.
What to do right now
- Decline the format. On the camera and on the computer, every time it asks.
- If the camera offers to repair or fix the card instead, decline that too. Treat it the same as a format.
- Take the card out of the camera and don’t shoot on it.
- Try the card once in a different reader, plugged straight into the computer. Readers fail more often than cards do. If the files appear, copy all of them off before doing anything else.
- If it still asks to be formatted, stop there. Don’t run CHKDSK, First Aid or any other repair tool on it.
What’s realistically recoverable
If the card still reads and nothing has been written to it since the message appeared, this is usually a Standard recovery.
I copy the whole card first, then work on the copy. When the damaged index can be read or repaired, files come back with their names, dates and folders. When it can’t, I find the files by their contents instead. Photos generally come back well that way. Video is harder, because long recordings are more likely to be stored in pieces.
You get a report of what I found, with file types and date range, before you decide anything.
When it isn’t
- The card was formatted and then used. Anything new that was written sits on top of something old. The overwritten part is gone. The rest may still be there. See accidentally formatted card.
- The card is failing, not just confused. If the message appeared because the card is wearing out, parts of it may not read at all, and the recovery will be partial.
- A repair tool has already run. These sometimes delete or truncate the files they can’t reconcile. What’s left is what I can work with.
- The card stops being detected. If no reader or camera can see it at all, that’s a physical case. Some of these I can do at my bench, quoted after evaluation. The rest I refer out, at no charge. See card not recognized.