A drive that opens but will not let you copy, save, or delete files may be locked physically, formatted for the other operating system, marked read-only by Windows, or protecting itself because of file-system or hardware trouble.
These steps apply to USB hard drives, SSDs, and flash drives on Windows and Mac.
Does This Affect You?
Use this if the drive mounts but Windows or Mac says it is read-only, access is denied, or you do not have permission to write.
Check the Basics
- Look for a physical lock switch on the drive, enclosure, or SD adapter and set it to unlocked.
- Unplug the drive and try another USB port.
- Test the drive on another computer.
- Check whether you lack permission for one folder rather than the whole drive. On Windows use Properties; on Mac use Get Info.
Fix Cross-Platform File System Limits
- Check the file system. On Windows, right-click the drive and open Properties. On Mac, select the drive and press Cmd+I.
- APFS and HFS+ are Mac formats that Windows can usually read only with extra software.
- NTFS is a Windows format that macOS can usually read but not write by default.
- For regular Windows and Mac use, back up the drive and reformat it as exFAT.
Reformatting erases the drive. Back up anything important before formatting. If you cannot format now, use trusted third-party NTFS or Mac file-system drivers temporarily.
Clear a Windows Read-Only Attribute
Be careful with diskpart. These commands affect a whole disk. Double-check the disk number against capacity before selecting anything.
- Right-click Start and open Terminal (Admin) or PowerShell (Admin).
- Type diskpart and press Enter.
- Type list disk.
- Identify the external drive by size.
- Type select disk N, replacing N with the correct disk number.
- Type attributes disk clear readonly.
- Type exit, then eject and reconnect the drive.
Check for File-System or Drive Failure
- On Windows, right-click the drive > Properties > Tools > Check.
- On Mac, run Disk Utility First Aid.
- If read-only mode returns after reconnecting, copy important data elsewhere immediately.
- Read-only behavior plus slow response, clicking, disconnects, or corrupted files can mean the drive is failing.
Sources
- Microsoft Support: Fix USB drive read-only
- Apple Support: Cannot add change or delete files on a disk
- Seagate Support: External drive read-only troubleshooting
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