Macintosh HD, or the MacBook internal hard drive, is basically the startup drive of most Apple computers. That means if your Mac or MacBook Pro can’t mount its startup disk, it is likely that you will experience problems, like your computer gets stuck on the login screen or it does not boot at all. Situations like this can be very annoying, especially if you have critical and important files stored on the “unmountable” hard drive.

• My Book Duo Won 27t Mount On Mac Osx
• My Book Duo Won't Mount On Mac Catalina

I have a 1 TB WD external HD that won't mount. I connect it via firewire to my MacBook Pro running OS 10.13 High Sierra. My mac sees the drive, it just won't mount. I've also tried to mount it via USB, but again, my system sees the drive, but won't mount it. Does anyone have any suggestion what I can do? When you try to plug in the drive again, your Mac no longer sees it. It won’t mount at all and acts as if it’s utterly invisible to macOS. In many cases, the only way to solve this problem is to completely remove the external drives and then restart your MacBook or Mac several times until the drives finally show up again. Brand New ExFat Formatted WD My Book Duo (16 Tb- 2 x 8 TB) will not mount on late 2012 MacBook Pro Retina running OS Sierra (version 10.12.2). The Drive appears in the following locations: System ReportUSB and Disk Utilities (where it is grey) but will not mount. Clicking the Mount icon in Disk Utilities would not mount it.

Fret not, because we will teach you what to do if your MacBook Pro won’t mount its startup disk. But before we do that, you better have a backup of all your data.

Backup, Backup, Backup!

Before you proceed with fixing the problem, it is best that you back up all your data first. That way, you can easily retrieve or recover your important documents and files in case something goes wrong.

Now, you might be wondering if it is possible to create a backup of your data, especially that your Mac is not even booting. Here’s what you should know: your Mac has a built-in Disk Utility, which can be accessed before startup. To use this, follow the steps below:

1. Get an external hard drive and connect it to your Mac.
2. Switch off your Mac. After five seconds, switch it back on.
3. After hearing the startup sound, press the CMD and R keys. Hold them until the Apple logo appears.
4. The macOS Utilities window will now appear.
5. Choose Disk Utility and hit Continue to proceed.
6. You can now start backing up your data using the external drive. Once you have backed up all your data, you can try a few fixes to your “unmountable” hard drive problems.

4 Fixes to a MacBook Pro That Can’t Mount Its Startup Disk

In most cases, mounting is an automatic process that happens as soon as the hard drive is connected to a Mac or MacBook Pro. Then again, drive mounting can be performed manually using the Disk Utility of your machine. It will be discussed further below.

Going forward, assuming you already have a backup of your important files and data, let’s proceed with resolving the problem. Below are a few ways to fix a MacBook Pro that can’t mount its startup disk:

1. Fix Your Hard Drive.

Sometimes, restarting your Mac is more than enough to fix the problem. However, if that does not work, then you might want to look into the angle that there might be something wrong with your hard drive. If that is the case, you have to boot your MacBook Pro in Recovery Mode via Disk Utility.

To hopefully fix your hard drive, follow these steps:

1. Switch off your MacBook Pro.
2. Turn it back on by pressing the Power button. But while doing that, press the CMD and R keys as well until the Apple logo appears.
3. The macOS Utilities window will open. From there, select Disk Utility.
4. From the left pane, choose your MacBook Pro hard drive.
5. Navigate to the First Aid tab.
6. Click the First Aid button to start fixing your drive.
7. Wait for the process to finish before restarting your machine.

2. Run Your MacBook Pro in Safe Mode.

When booted in Safe Mode, your MacBook Pro will start only with the minimum requirements and utilities needed. All other programs and apps that are unnecessary will never be loaded. Hence, if the reason why your startup disk cannot be mounted is a faulty app or program, booting your MacBook Pro in Safe Mode might just fix your problem.

To run your MacBook Pro in Safe Mode, do these:

1. Restart your MacBook Pro.
2. After you hear the startup sound, press the SHIFT key immediately. Continue holding it until the Apple logo appears.
3. If your MacBook Pro boots up properly, then uninstall any program or app you suspect is causing the problem.
4. Restart your machine.

3. Disconnect All External Peripherals.

It is possible that a faulty peripheral connected to your MacBook Pro could be causing your startup disk problems. To verify this, follow the steps below:

1. Switch off your machine.
2. Disconnect all external peripherals connected to your MacBook Pro, including printers, external hard drives, USBs, and scanner. You may leave the keyboard and mouse attached in the meantime.
3. Switch on your Mac. If it boots properly, then one of the peripherals is causing the problem.
4. Identify the exact cause of the problem by connecting each of the peripherals one by one. Make sure you reboot your MacBook Pro every time you connect a peripheral.

4. Reset the SMC and PRAM.

This may sound like a technical solution, but it isn’t. In fact, resetting the SMC and the PRAM takes only a few seconds.

To reset the PRAM and SMC, follow these instructions:

1. Reboot your MacBook Pro.
2. After you hear the startup sound, press the Option, CMD, P, and R keys. Hold them until you hear the second startup tone.
3. Release the keys. Your PRAM will then be reset.
4. Restart your MacBook Pro and check if the problem persists.
5. If resetting the PRAM does not fix the problem, try resetting the SMC. Start by shutting down your MacBook Pro.
6. Plug your machine into a wall outlet.
7. Next, press the CTRL, SHIFT, Option, and Power keys for 10 seconds and release them together.
8. Restart your MacBook Pro and see if it worked.

How to Mount a Startup Disk on MacBook Pro

At this point, you probably want to know how to properly mount a startup disk on your MacBook Pro to avoid problems in the future. Well, mounting a startup disk does not literally suggest physically setting it up with all the wires. It simply means making the startup disk available for your system to perform different read and write operations.

If the startup drive is in good shape, your system Disk Utility should see it. Under the Disk Utility window, select your preferred startup disk. Click on it to mount. By now, your new startup disk should be accessible by your operating system.

What’s Next?

Now that you know how to deal with your “unmountable” startup disk problem, it’s time that you get your MacBook Pro running fast and smooth by downloading and installing a reliable tool like Outbyte MacRepair. Not only will this tool allow you to conveniently find and fix speed and stability problems, it will also protect your privacy. What more can you ask for from such a powerful tool?

If you know other ways to fix a MacBook Pro that can’t mount its startup disk, please share them with us below. We’re looking forward to hearing from you.

Summary: This post introduces 5 solutions you can try when you are unable to mount an external hard drive on your Mac. Also, to avoid further data loss, you can use iBoysoft Data Recovery for Mac to recover lost data from this unmountable external drive first.

After you connect an external hard drive to your Mac, if everything is working fine, the operating system will automatically recognize, read, and mount your external drive, as well as show it in the Finder and on the desktop.

However, if your disk gives up the ghost just like the users below, the external disk will not be showing up as normal. And if you check it in the Disk Utility, you will find your drive unmounted there.

'I was able to use my 3 TB external hard disk drive to backup my data last week. But now it doesn't mount after I migrate from Mojave to macOS Catalina. I dug around and tried a lot of stuff but still can't mount this external hard drive on my Mac. Can someone explain how to get this drive mounted so I don't lose the data?'

Why an external drive is not mounting on Mac?

There are numerous reasons for the external hard drive not mounting issue. The following are a few of the most common ones:

Hardware and connectivity issue

Most of the time, you can't mount your external drive on a Mac just because the connectivity is not in proper condition. This issue may be affected by a loose fitting, a broken USB cable, the wear on USB ports, etc.

Sometimes, such connectivity issues could make your external drives keep disconnecting, or much worse, it would make your external hard drive unmountable eventually. After all, it is essential to have a firm and tight connection.

Corrupted disk

Another possible reason for an unmounted disk may come from the problematic hard drive itself. Wonder how could it be? Well, it is possible that you're unable to mount a drive just because it is corrupted and unrecognizable by macOS.

You can recall if your external drive has experienced one of these things: an unsafe removal when you are transferring files, an improper ejection, a sudden power outage, or even a virus infection. If so, your disk might be corrupted and it should be the culprit that you are unable to mount your external drive probably.

Incorrect formatting of the disk

In some cases, an unsupported file system will make your external drive unmountable. It is reasonable because if your Mac can't even read your disk's file system, how can you mount and access this hard drive on your Mac? This factor may not be as possible as the other causes, but it does happen.

Unable to mount external hard drives on Mac, how to fix?

Even though the reasons for a not mounting disk are different from case to case, certainly there are some things you can do to fix this issue. The following are five effective solutions to the 'external hard drives won't mount on Mac' issue, and some of them are just basic checks.

Solution 1: Check and fix connectivity issues

The first thing you can do is to make sure that your disk is connected to your Mac properly.

If you are not sure if there is a problem with the USB port/hub, you can plug a working external drive in to a port/on a hub, unmount and eject it. Then plug the unmountable external hard drive into that port/hub.

Also, here are some things you can try.

• 1. Reconnect your external hard drive to your Mac and ensure that it fits the USB port snugly.
• 2. Connect the external hard drive to a different USB port or a different Mac.
• 3. Replace the USB cable or adapter in case that it was damaged or broken.
• 4. Connect it to a Windows PC and see if the storage device is powered on and working.

Solution 2: Check the file system of the external hard drive

Well, if you don't know exactly what file system your disk is formatted with while your external hard drive can't be mounted now, you can go to Disk Utility to have a check if it is formatted with an unsupported file system.

Remember that macOS is friendly with APFS and HFS+ and is in a neutral attitude with FAT, FAT32, and exFAT. However, it is a different story if you need to access and write to NTFS file system on Mac. By default, macOS only enables NTFS drive read support but disables write support. In this case, you can download a free NTFS driver for macOS to mount this external hard drive in read and write mode.

Still unable to mount the external hard drive on Mac? Then it should be some problems with the drive itself. Then you can go with the following solutions to troubleshoot this problem.

Wait! Have you recovered your important data from this unmountable drive?

Before you go any further to fix this unmountable hard drive, you'd better make sure you have backed up your data on this drive to avoid data loss. The reason is that when your external drive won't mount, you lose the only access to all your files on this drive.

In this situation, if you have important files on the external hard drive, any operations on the drive could overwrite the original data and cause irreparable data loss.

Forget to back up before? You can also use Mac data recovery software like iBoysoft Data Recovery for Mac to recover lost data from the unmountable external hard drives.

iBoysoft Data Recovery for Mac is a free external hard drive data recovery tool that enables you to recover lost data from external drives, especially when a hard drive is unmounted, formatted, inaccessible, unreadable, or corrupted.

It's fully compatible with macOS Big Sur 11/Catalina 10.15/Mojave 10.14/High Sierra 10.13/10.12 and Mac OS X 10.11/10.10/10.9/10.8/10.7. In addition to external hard drive data recovery, it also can recover lost data from internal Mac hard drives, USB flash drives, SD cards, memory cards, pen drives, etc.

Tutorial to recover lost data from unmountable external drive on Mac with iBoysoft Data Recovery for Mac

• 1. Download and install iBoysoft Data Recovery for Mac on Mac, and then restart the computer.
• To use iBoysoft Data Recovery for Mac, you need to install this software on your Mac. You can just download the installation package and install it with no fuss.
• 2. Launch iBoysoft Data Recovery for Mac.
• After successfully downloading this program on your Mac, you can drag it to your Applications folder to install it, or you can double-click its icon to launch it.
• 3. Select the unmountable external drive and click Scan button to scan all lost data.
• When the Mac data recovery software is launched, all connected storage devices will be listed in the interface. You can see the name, file system, and space allocation of your hard drives and partitions. Locate your unmounted external hard drive, select it, and click 'Scan' to scan for lost data.
• Two scanning modes are allowed: Quick scan and Deep scan. Quick scan mode saves time for users and is applied when data is recently deleted. Deep scan mode finds more files at the cost of more time, and it's used when file system is corrupted or partition table is lost. Anyway, this software will automatically choose the most efficient way to scan for files according to the disk condition.
• 4. Preview the searching results, choose files you need, and click Recover to get them back.
• With the preview feature, you can check whether your files on this unmountable disk are in a good condition or not. It saves time and money for users. The software will show if your file is corrupted so that you would not waste energy to recover it or pay for this data recovery product.
• 5. Have a check to ensure you have got all lost data back.

Now you either have a copy of a data backup in hand, or have recovered your important files with iBoysoft Data Recovery for Mac. Therefore, you can go ahead to repair this unmounted external drive without worrying about data loss.

Solution 3: Repair the external hard drive with Disk Utility

When an external hard drive is not working properly, you can use the built-in disk repair tool - First Aid to check and repair disk errors.

• 1. Launch Disk Utility.
• 2. Choose the unmountable external drive on the left sidebar.
• 3. Select First Aid in the top center and click Run.

Solution 2: Repair the external hard drive with Terminal

Sometimes, Disk Utility may not function as desired. Fortunately, you can still try to repair the corrupted external hard drive with Terminal.

My Book Duo Won 27t Mount On Mac Osx

• 1. Go to Applications > Terminal
• 2. Enter: diskutil list (This will list out the available volumes).
• 3. Check the volume identifier from the table that appears.
• 4. Enter: diskutil repairVolume [diskvolume identifier]. For example, if the volume identifier of an external hard drive is disk2s, you should enter: diskutil repairVolume disk2s.

Solution 3: Reformat the external hard drive

If yourexternal hard drive can't be repaired with Disk Utility and Terminal, the file system of this drive might be seriously corrupted. The only way to fix this unmountable external drive is to reformat it.

Warning: Reformatting will erase all data on the external hard drive, so please make sure you have backed up important data.

• 1. Launch Disk Utility from Utilities.
• 2. Click the icon of the unmountable external drive on the left part of the window.
• 3. Click the Erase function on the top of the Disk Utility window.
• 4. Complete the related information (name, format, scheme), then click Erase button.

Conclusion

When you can't mount an external hard drive on your Mac, you can try the 5 methods introduced in this post. But no matter which solution you are going to try, to avoid data loss, you are always advised to back up your files or recover your data from this unmountable drive first with iBoysoft Data Recovery for Mac.

But if unfortunately, none of these solutions can make your hard drive work again, or your disk is not even detected or showing up in Disk Utility, then this drive might be physically damaged. Under this situation, you should send it to a local disk repair service and see if they can help.

My Book Duo Won't Mount On Mac Catalina

Good luck!