Why can’t I copy files to external hard drive Mac?

Trying to copy files from your Mac to an external hard drive, but find that your files won’t copy over? There are a few reasons why you may be unable to copy files from your Mac to an external hard drive.

Common Reasons You Can’t Copy Files to External Hard Drive on Mac

Here are some of the most common reasons you may be unable to copy files to an external hard drive on your Mac:

  • The external hard drive is formatted incorrectly or incompatible with Mac
  • There is not enough storage space on the external hard drive
  • The external hard drive is corrupted or damaged
  • There are permission or sharing issues with the files you want to copy
  • The external hard drive is locked or read-only
  • The USB port or cable connecting the hard drive is faulty
  • There is an issue with the Mac’s hard drive itself

Let’s explore each of these potential issues in more detail.

External Hard Drive Format Is Incompatible with Mac

One of the most common reasons you may be unable to copy files from your Mac to an external hard drive is because the drive is formatted incorrectly for the Mac operating system.

By default, Windows PCs format hard drives in NTFS format, while Macs use HFS+ format. Trying to copy files between these two formats can cause errors or make the files unreadable.

If your external hard drive is formatted for Windows (NTFS), your Mac will be unable to write files to it. You’ll only be able to read files already on the drive.

To fix this, you need to reformat the external hard drive to a Mac compatible format like HFS+ or exFAT. Reformatting will erase any existing data on the drive, so be sure to back up your files first.

Here are the steps to reformat an external hard drive on Mac:

  1. Connect the external hard drive to your Mac using the USB cable.
  2. Open Disk Utility (located in Applications > Utilities folder or searchable in Spotlight).
  3. Select the external hard drive in the left sidebar.
  4. Click Erase at the top.
  5. Choose a compatible format like Mac OS Extended (Journaled) or exFAT.
  6. Give the drive a name and click Erase to reformat it.

Once your drive is reformatted for Mac, you should be able to copy files to it properly.

Not Enough Storage Space on External Hard Drive

Another reason you may be unable to copy files from your Mac to an external drive is because the drive is full or does not have enough free space.

Just like on your Mac’s internal hard drive, an external drive needs sufficient free space for new files to copy over successfully. If the drive is nearing full capacity, macOS may block you from writing more data to it.

To check how much free space is left on your external drive:

  1. Connect the drive to your Mac.
  2. Open Finder and click on the external hard drive in the sidebar.
  3. Look at the storage space details shown at the bottom of the Finder window.

If the drive is almost full, you’ll need to free up space before you can copy more files over. Try deleting unused files, moving data to other drives, or formatting the external drive to completely wipe it.

As a rule of thumb, aim to keep at least 10-20% of your drive space free at all times to prevent file copying issues.

External Hard Drive Is Corrupted or Damaged

If your external hard drive is corrupted or physically damaged, that could prevent your Mac from being able to access it and copy files over.

Signs of a corrupted or damaged drive include the drive not appearing at all in Finder or Disk Utility, frequent error messages when accessing the drive, or the drive making strange noises.

To troubleshoot, try connecting the external drive to another computer to see if the same issue occurs. If the drive works fine on another computer, then the problem is with your Mac. But if the drive continues to have issues, then it’s likely corrupted or damaged.

To fix a corrupted external drive:

  1. Open Disk Utility and run First Aid on the drive. This checks for errors and attempts repairs.
  2. Reformat the drive after backing up your data. Reformatting completely rewrites the drive.
  3. If errors persist, your drive may be physically damaged. Contact a data recovery service or replacement.

Avoid disconnecting external hard drives without properly ejecting them first to prevent corrupting the drive. Also make sure to use the Remove Safely option before disconnecting.

Permission and Sharing Issues

The permission and sharing settings on your files can also prevent copying them to an external drive.

By default, new files saved to your Mac have Read & Write permission for your user account. If you change permissions to Read Only or restrict sharing access, you may get errors when trying to copy those files elsewhere.

Check the permission and sharing settings on any files that won’t copy over. Make sure you still have Read & Write access to them. You can change permissions in Finder by right-clicking a file, selecting Get Info, and adjusting settings in the Sharing & Permissions section.

Also check your external drive permissions. If permissions on the entire drive are set to Read Only, you can’t make any changes by copying files over. Open Disk Utility, select your drive, click the Erase tab, and ensure permissions are set to Read & Write.

External Hard Drive Is Locked or Read-Only

Some external hard drives have a physical lock switch on them that can lock the drive and prevent files being written to it. This is useful to protect important data from accidental changes. But it can also stop you copying files over if the drive is locked.

Check your external hard drive for a sliding lock switch. Unlock the drive before attempting to copy your files to it. This should immediately fix any read-only errors you’re getting.

In Disk Utility, you can also check that a drive is not set to Read Only by selecting it, clicking the Erase tab, and verifying Read & Write access under Permissions.

USB Port or Cable Connection Issues

Sometimes there may not be anything wrong with either your Mac or the external hard drive – the issue is with the physical USB connection between them.

If the USB cable or port you are using to connect the drive is faulty, damaged, or disconnected, your Mac may be unable to mount the drive properly for file transfers.

Try plugging the drive into a different USB port on your Mac. Use a different cable if you have one available. Test connecting other devices with the same cable/port to see if the issue persists.

If you notice slow transfer speeds in addition to file copying errors, the USB connection is likely at fault. USB cables degrade over time. Inspect your cable for any cuts, crimps or damage. Replace damaged cables with a high-quality new one.

For fastest speeds, use a USB 3.0 cable with USB 3.0 ports. Avoid daisy chaining multiple devices as this can affect power delivery. If available, plug the drive directly into your Mac rather than through a USB hub.

Issues with Mac’s Hard Drive

In some cases, the issue preventing file copying lies with your Mac’s hard drive itself rather than the external one.

If your Mac’s hard drive is almost full, corrupted, or has permission issues of its own, you may encounter errors trying to access and move data from it.

Try checking your system hard drive health using Disk Utility. Look for permission problems with System Information. Running disk repair tools like First Aid could help resolve problems that prevent copying files from that drive.

It’s a good idea to regularly backup your Mac’s hard drive anyway to avoid data loss if it becomes corrupted or fails. Time Machine makes this easy to do using an external drive as the backup destination.

How to Copy Files to External Hard Drive on Mac

When you’ve resolved the above issues preventing file copying, here is how to properly copy files from your Mac to an external hard drive:

  1. Connect the external drive to your Mac using a USB cable. Make sure the drive mounts successfully on the desktop.
  2. Open Finder and navigate to the files/folders you want to copy. Select them.
  3. Drag the selected files over to the external hard drive icon shown in Finder sidebar.
  4. The files will now copy over to the external drive location.
  5. Alternatively, you can right-click files, select Copy, then right-click external drive and select Paste.
  6. Use Finder’s progress bar to monitor the transfer status.
  7. Eject the external drive safely once copying finishes.

Following these steps prevents errors and ensures files copy over successfully from Mac to external drive. Remember to eject properly after disconnecting.

Tips for Using External Hard Drives on Mac

Here are some additional tips for using external hard drives with your Mac:

  • Always eject and safely disconnect external drives before unplugging them to prevent data loss or corruption.
  • Regularly backup your Mac’s internal drive to external storage for redundancy.
  • Use newer, faster connections like USB-C or Thunderbolt when available for quicker transfers.
  • Partition large external drives so a portion is compatible with Mac and PC for universal use.
  • Avoid using external drive for Time Machine backups as constant rewriting wears them out quicker.
  • Look for external SSD drives which are faster than HDD drives with moving parts.


While external hard drives provide vital expanded storage for Macs, you may encounter occasional issues copying files over. Faulty permissions, drive errors, lack of space, and physical connection problems are the most common culprits.

Carefully checking each potential point of failure can help identify and resolve the issue, allowing proper file transfer between your Mac and external drive. Following best practices for drive care and maintenance will prevent many problems from occurring in the first place.

With robust storage capacity and portability, external hard drives will continue playing an important role in a comprehensive Mac backup strategy. Understanding common copying problems helps ensure you can always access those crucial files.