Unable to copy files from Mac to external hard drive: How to fix

Keep bumping into the unable to copy files from Mac to external hard drive error message? This seriously blocks backup workflows, file transfers, and data organization.

When we encounter external drive issues, it’s not surprising that most of us panic about our data. The good news is that most copy failures are simple, and you shouldn’t need to erase the drive.

Why won’t files copy to an external drive?

Most times, it’s not some mysterious Mac meltdown. It’s one of a few predictable causes:

• The drive is full.

• Connection problems with cables or adapters.

• Permissions are blocking writes.

• Format isn’t playing nicely with macOS.

• The disk has errors.

• Occasionally, it’s encryption, and you’re missing the password.

Knowing where your issue falls is actually pretty important, because I’ve watched people wipe a drive thinking it was corrupted when the real issue was NTFS, which macOS often treats as read-only. That mistake hurts.

How to fix it if unable to copy files from Mac to external hard drive

Quick checks first

Before you do anything, work through this troubleshooting checklist. It can save you a ton of time.

1. Make sure your cable or adapter is not damaged.

2. Test another or try a different port if you can.

3. Check if the drive is recognized in Finder (if not visible, it’s a connection issue)

4. Check if your external drive has a physical lock switch, and unlock it if it's locked.

5. Test copying a small file first to rule out file-specific issues.

6. Restart your Mac to clear temporary glitches.

If you’re still unable to copy files from a Mac to an external hard drive, it’s time to move on to the more detailed, specific fixes.

Check your drive’s capacity and free up space

Many copy failures are simply storage limits; here’s what to do:

1. In Finder > right-click the drive > Get Info.

2. Check Available space.

Your macOS needs room to complete transfers. If I am moving 50GB, I want slightly more than 50GB free. If the drive is nearly full, delete unnecessary files.

If the drive looks empty but still refuses copies, that is a red flag for corruption (move to the next section).

Before moving large files, run the My Clutter feature from CleanMyMac to identify which files on your Mac are taking up the most space. This helps you prioritize what to move and avoid transferring unnecessary duplicates or large old files that waste external drive space; here’s how:

1. Open CleanMyMac — get your free trial here (seven-day free).

2. Select My Clutter > Select your External Drive > Scan.

3. Click Review All Files.

4. Delete what’s taking up space.

Check permissions & drive format compatibility

1. Right-click the drive in Finder > Get Info.

2. Under Sharing & Permissions. My account must show “Read & Write.” (If it is greyed out, unlock the padlock and update it.)

3. Now, look under Format:

• NTFS -  Allows read but blocks write on macOS.

• exFAT works on both Mac and Windows.

• APFS or Mac OS Extended are best for Mac-only use.

4. If the format is incompatible, reformatting fixes it, but this erases everything. You will first need to back up any important files to a Cloud storage or your Mac.

5. Open Finder> Utilities> Disk Utility > Select the drive and press Erase > choose exFAT or APFS.

If you’re copying loads of files and the process is slow or failing intermittently, Mac cache or app processes may be causing the problem. Use two features from CleanMyMac to help: Cleanup and Performance. These can resolve speed and stability issues without reformatting.

Check for disk corruption or encryption

Encrypted Drives

If your external drive shows a lock icon in Finder when it’s mounted, it is encrypted. You’ll need to enter the password. Without it, reformatting is the only option, which deletes data.

Corrupt Drive

1. Open Disk Utility.

2. Select the drive.

3. Click First Aid. Run repair.

If First Aid fails repeatedly, the drive may have file system damage or hardware issues.

Reformat your Drive

This is a last resort, and only after backing up, will it erase everything. You can use Disk Utility to reformat the drive — just click Erase and fill everything out in the window that pops up.

Prevent future copy issues

1. I keep at least 10-15% free space on external drives. Full drives corrupt more easily.

2. Make sure you always eject your external drives properly instead of pulling the cable mid-save.

3. Keep your macOS updated. Tahoe updates through 2026 have improved file system stability.

4. Check drive health periodically in Disk Utility.

5. Avoid cheap adapters when transferring large volumes of data.

6. Back up your external drives periodically.

File transfer glitches can also be prevented by maintaining your Mac’s overall performance. Smart Care from CleanMyMac can clear cache, remove temporary files, and optimize system performance, all known factors that improve file transfer speeds and reliability to external drives. A healthy Mac transfers files faster and more reliably.

When to seek professional help

• If First Aid fails repeatedly, that suggests hardware damage.

• Clicking noises indicate a problem; stop usage immediately.

• If it appears but refuses to mount or eject properly, deeper file system corruption may exist.

• If the data is critical, contact a data recovery specialist before attempting further fixes.

That's how to handle it if you're unable to copy files from a Mac to an external hard drive.