TL;DR
This Mac error means it can’t read the drive’s file system, or the drive isn’t responding. Click Ignore, not Initialize, because Initialize erases the drive. Then check the cable and port, look for the drive in Disk Utility, run First Aid, and test another computer. Erase and reformat only as a last step, after your files are safe.
A pop-up appears the moment you plug in your drive: “The disk you attached was not readable by this computer.” It means your Mac can’t read the drive’s file system, or the drive isn’t responding. Click Ignore, not Initialize, because Initialize erases the drive. Then check the cable, run First Aid, and test another computer. Many unreadable drives can be repaired, or their files saved, if you act carefully.
What Does This Error Mean?
The message pops up when macOS detects a drive but can’t mount it. Mounting means making the drive’s contents appear in Finder. A drive has a file system, which is the system that organizes files on it. If the Mac can’t understand that system, it shows this error.
The pop-up gives you three buttons:
What Do These Mac Buttons Do?
Understand each option before you act on an unreadable drive.
| Button | What it does | Safe if the drive has data? |
|---|---|---|
| Initialize | Opens Disk Utility, where you can erase or reformat the drive. | No — avoid erasing Erasing deletes existing data. |
| Ignore | Closes the message and leaves the drive as it is. | Yes Does not erase the drive. |
| Eject | Disconnects the drive from the Mac. | Yes Does not erase the drive. |
If the drive contains important files, don’t erase or reformat it. Choose Ignore for now and investigate the cause before making changes.
Why does this error appear?
Several things can cause it:
Why Your Mac Can’t Read the Drive
Common causes, what’s happening, and whether your files are at risk.
| Cause | What’s happening | Data at risk? |
|---|---|---|
| A brand-new, unformatted drive | The drive has no file system yet. | No, it’s empty |
| Damaged file system | A crash or unsafe unplug corrupted the drive’s index. | Yes — data may be at risk |
| Unsupported format | The drive uses a format macOS can’t open, like Linux ext4. | Not necessarily — another tool may be needed |
| Encrypted drive | A Windows BitLocker drive may need a compatible tool and key. | Not necessarily — access requires a key |
| Bad cable, port, or hub | The connection drops or the drive lacks power. | Usually no |
| Failing drive | The hardware is wearing out or damaged. | Yes — data may be at risk |
If the drive contains important files, don’t erase or reformat it. If it makes unusual noises or repeatedly disconnects, stop using it to reduce the risk of further damage.
New drives often show this message. That’s normal, and you can format them. But if the drive holds files you care about, treat it as a risk until you know more.
What Should You Do First?
Take these safe steps before you try any fix:
- Click Ignore. Don’t click Initialize.
- Decide if the data matters. If it does, avoid anything that writes to the drive.
- Unplug and reconnect. Check whether the drive lights up or spins.
- Use the same Mac to compare results.
Why avoid Initialize? Because it leads straight to the Erase option. One wrong click can delete every file on the drive.
How Do You Fix a Disk That Is Not Readable on a Mac?
Work through these in order. The first fixes carry no risk to your files.
Fix 1: Check the cable, port, and power
- Try a different cable. Cables fail often.
- Try another port, and plug straight into the Mac, not a hub.
- Give the drive enough power. Some hard drives need their own power adapter or a powered hub.
- Remove adapters, if you can.
Fix 2: Restart the Mac and update macOS
A restart clears small glitches. Also open System Settings, then General, then Software Update, and install updates. Updates can improve drive support.
Fix 3: Look for the drive in Disk Utility
- Open Disk Utility from Applications, then Utilities.
- Click View, then Show All Devices.
- Look for your drive in the sidebar. It may be listed even if it’s not in Finder.
- If you see a gray volume, select it and click Mount.
If the drive doesn’t appear at all, hold Option and click the Apple menu, then choose System Information. Open the USB section and check whether your Mac sees the hardware. If it doesn’t, suspect the cable, the port, or the drive itself.
Fix 4: Test the drive on another computer
Plug it into a different Mac or a Windows PC. If it works there, the drive is probably fine, and the problem is your Mac’s settings, port, or the file system. If it fails everywhere, hardware failure is more likely.
Fix 5: Run First Aid
First Aid checks and repairs file system errors. Apple’s instructions say to run it in this order: each volume, then each container, then the physical drive.
- Open Disk Utility, then click View, then Show All Devices.
- Select the volume, then click First Aid, then Run.
- Repeat for the container, then the physical drive.
If your files are valuable, note this. First Aid can change file system structures. For a drive with irreplaceable data, consider a professional recovery service before you run repairs.
[OUTBOUND LINK SUGGESTION: link “Apple’s instructions” to ]
Fix 6: Mount or check the drive in Terminal
Use this if Disk Utility shows the drive but won’t mount it.
- Open Terminal from Applications, then Utilities.
- Type diskutil list and press Enter. Find your external drive and its identifier, like disk4.
- Try to mount it with diskutil mountDisk /dev/disk4.
- Check it with diskutil verifyDisk /dev/disk4.
- If it reports errors, you can try diskutil repairDisk /dev/disk4.
Replace disk4 with your drive’s real identifier. Don’t use your Mac’s internal disk. Double-check the name and size before you press Enter.
Fix 7: Check the file system format
Which Drive Formats Does Mac Support?
Compare file systems, read and write compatibility, and important notes before troubleshooting your external drive.
| Format | Mac can read? | Mac can write? | Notes |
|---|---|---|---|
| APFS | Yes | Yes | Best for Mac-only SSDs. |
| Mac OS Extended (HFS+) | Yes | Yes | Good for older Macs and hard drives. |
| exFAT | Yes | Yes | Works on Mac and Windows. |
| FAT32 | Yes | Yes | Widely compatible, but individual files are limited to 4 GB. |
| NTFS | Yes | No, by default | Windows format. File-system damage can prevent the drive from mounting. |
| ext4 (Linux) | No, natively | No, natively | Requires compatible third-party software or another supported system. |
| BitLocker-encrypted | Not natively | Not natively | Usually requires Windows or compatible software and the correct unlock key. |
If the drive contains important files, don’t initialize or reformat it just because your Mac can’t read it. First check the cable, connection, file system, and drive health. Back up accessible data before making changes.
If your drive uses a format the Mac can’t open, the drive isn’t broken. It needs a different computer or tool, or a reformat.
Fix 8: Recover your files before you erase anything
If the drive holds important files, save them first:
- Connect the drive to a Windows PC or another computer that can read it, then copy the files.
- Don’t write new files to the drive.
- If you hear clicking or grinding, stop and contact a data recovery professional.
- Consider a professional recovery service for valuable data, since DIY tools can sometimes make things worse.
Fix 9: Erase and reformat as a last resort
Erasing deletes everything. Only do it if the drive is blank, or you’ve saved your files.
- Open Disk Utility, then View, then Show All Devices.
- Select the physical drive at the top, not just the volume under it.
- Click Erase.
- Name the drive, and pick a format: APFS or Mac OS Extended for Mac-only use, or exFAT to share with Windows.
- For Scheme, choose GUID Partition Map.
- Click Erase and wait.
If erasing fails, the drive may have a hardware fault.
What if the drive keeps failing?
Watch for these signs of real failure:
- Clicking, grinding, or beeping sounds
- A drive that never spins up
- A drive that disappears from every computer
- Very slow copying with repeated errors
If you see them, stop using the drive. Back up anything you can, and replace it.
Which Tips Fit Your Type of Drive?
| Drive Type | Extra Tips |
|---|---|
|
USB Flash Drive
|
Try another port and a different Mac. Unsafe removal is a common cause. |
|
SD or Camera Card
|
Try another card reader. Reformat in the camera only after saving your photos. |
|
External Hard Drive
|
Check the power supply and cable. Listen for clicking, which may indicate a hardware problem. |
|
External SSD
|
Check the cable and enclosure. Update the drive’s firmware if the manufacturer offers it. |
How Can You Prevent This Error?
- Eject drives properly. Don’t unplug during a copy.
- Use the right format. Choose exFAT for sharing, and APFS or Mac OS Extended for Mac-only drives.
- Back up regularly. Keep two copies of important files, and one off-site or in the cloud.
- Avoid cheap hubs and worn cables.
- Replace old drives before they fail.
- Keep macOS updated.
- Test new drives with a few files before you trust them.
Conclusion
“The disk you attached was not readable by this computer” sounds serious, but the fix is often simple. Click Ignore first, then check the cable, look in Disk Utility, run First Aid, and test another computer. Erase the drive only after your files are safe.
If your drive holds something you can’t replace, slow down and protect it first. Then explore more Mac and storage guides at Techprixo, and share this article with someone who just clicked the wrong button.
FAQ
It means your Mac can’t read the drive’s file system, or the drive isn’t responding. The cause may be a new unformatted drive, a damaged file system, an unsupported format, a bad cable or port, or failing hardware. Click Ignore first, because Initialize erases the drive.
Not if the drive holds files you need. Initialize opens Disk Utility so you can erase and reformat the drive, and erasing deletes everything on it. Click Ignore instead, then try the cable, port, First Aid, and another computer. Choose Initialize only for a blank drive, or after you’ve saved your data.
Click Ignore, then try another cable, port, and computer. Open Disk Utility, choose View, Show All Devices, and run First Aid on the volume, container, and drive. If files are critical, recover them first or hire a professional recovery service. Erase the drive only after your data is safe.
A Mac can read NTFS drives, but it can’t write to them by default. Damage can stop an NTFS drive from mounting at all. For drives you share between Mac and Windows, exFAT is usually the easiest format. Formatting erases the drive, so save your files first.
Not always. Many cases come from a bad cable, a missing format, or file system damage. Signs of real hardware failure include clicking sounds, a drive that never spins up, or one that disappears from every computer. If you hear clicking, stop using the drive and contact a data recovery professional.