A drive that suddenly asks to be "formatted" or shows as RAW instead of its usual file system almost always has a corrupted file system table, not physically damaged storage — and that's recoverable with tools already on your computer, for free. The critical rule: don't write anything new to the drive, including running a "quick format," until you've tried to recover what's on it, since that overwrites the data you're trying to save.
01Stop and don't format
Windows and macOS will both prompt you to format an unreadable drive as soon as you plug it in. Decline that prompt. Formatting rewrites the file allocation table, and while the actual data often survives a quick format for a while, it makes recovery meaningfully harder and isn't necessary yet.
02Windows: run CHKDSK to check for file-system errors
chkdsk X: /f /rReplace X: with your drive's actual letter (check in File Explorer first). The /f flag fixes errors it finds, /r locates bad sectors and recovers readable information from them. This alone fixes the majority of "drive needs to be formatted" cases where the underlying storage is fine.
03macOS: use Disk Utility's First Aid
- Open Disk Utility (Cmd+Space, type "Disk Utility").
- Select the USB drive in the sidebar — the actual drive, not just the volume.
- Click "First Aid" and run it.
If First Aid reports it fixed the disk, try mounting it normally afterward.
04If the file system is too damaged to repair, recover files directly instead
Free tools that scan the raw drive for recoverable file signatures, bypassing the broken file system entirely:
- Windows: Microsoft's own free "Windows File Recovery" (from the Microsoft Store) works from Command Prompt and handles both NTFS and the FAT/exFAT format common on USB drives.
- macOS: Disk Drill's free tier recovers up to 500MB, enough to test whether your specific files are recoverable before deciding whether a paid tool is worth it.
Always recover files to a different drive — recovering onto the same damaged drive risks overwriting other recoverable data.
05How to tell if it's physical damage instead
If the drive isn't recognized at all (no drive letter, doesn't appear in Disk Utility, makes clicking sounds — rare for flash drives but possible on the controller chip), that's hardware failure, not file system corruption. No free software fixes that; it requires professional data recovery, which is expensive and only worth it for genuinely irreplaceable data.