I tried reset nvram, also use other port, I even test another bootable USB but it can be detected, just the external windows 10 USB drive not detect on MacBook Air during boot, but once boot in macOS It show up as external drive. Only filevault enable no firmware password etc. I hope you have a backup. Open Disk Utility and see if the hard drive shows there. If so, run repair disk until you get no errors. Try the install again. If that doesn't work, r eformat the drive using Disk Utility/Erase Mac OS Extended (Journaled), then click the Option button and select GUID. Then re-install the OS.
- Hard Drive Not Detected Mac
- External Hard Drive Not Recognized Mac
- Hard Drive Connected But Not Showing Up
- External Hard Drive Won't Show Up Mac
Summary :
Are you still troubled by the issue 'hard drive not showing up'? This article will show you how to slove the probelm 'hard drive not showing up'. In addition, the issue 'hard drive not showing up' may lead to data loss. But, don't worry! MiniTool Power Data Recover, a piece of profesional data recovery software, can help you to get the lost data back.
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Hard Drive Not Showing up
Hard drive containing massive important data is not showing up in My Computer or Windows Explorer? Have you ever encountered this problem?
It is believed that many users have encountered the situation mentioned above. Let's see a true example from answers.microsoft.com:
My 2nd hard drive isn't showing up in my computer. The hard drive was a slave I took out of my old XP machine after it crashed. I had installed it into my new vista machine before and it was working, but then I had to reinstall the OS and ever since then it has not shown up. I have double checked to make sure it was set as a slave drive and it is. It shows up in the Bios, the device manager, and in Disk Management, just not in my computer. Nothing is showing up as unallocated in disk management and the drive says it's healthy. In the device manager it says the device is working properly. I've tried to just give it a drive letter in disk management, but when I right click on it the only option I have is help. I've also tried to update the drivers, and it says they are up to date. I've tried disabling and enabling the hard drive. I've even tried uninstalling it. When I restarted it did detect it and reinstalled the drivers, but I still can't get it to show up in my computer. answers.microsoft.com
Why does hard drive (including external hard drive or, USB hard drive) not show up in My Computer or Windows Explorer? Do you know how to deal with this issue? Besides, can we recover data from hard drive when it is not showing up?
Want to know answers of these questions? Here we are!
Why Hard Drive Isn't Showing up and How to Fix
According to the questionnaire survey and the result of experiment, we find there are many factors that can cause the 'hard drive not showing up' issue, including mistaken operation, computer virus invasion, and hard drive letter missing, and so on.
Let's discuss the details.
Case 1- Hard Drive Is Not Initialized
As we know, once hard drive shows as uninitialized, we are unable to see it in Windows Explorer, and cannot access its files. And many reasons (such as virus invasion, master boot record corruption, bad sectors, and so on) can lead to disk not initialized issue.
Solution
To solve this issue, you can right-click the uninitialized disk, and then choose Initialize Disk to initialize it to use it again.
Note: During initializing process, you will be asked to initialize to MBR disk or GPT disk, as shown below. In this case, you can choose appropriate partition style according to actual needs. (Here, I guess, you might be interested in this post 'How to Convert MBR to GPT without Data Loss in Windows 7' since it not only explains what are GPT disk and MBR disk but also shows how to convert MBR disk to GPT.)
If your disk is not initialized anymore due to sudden change, we don’t suggest you to initialize the disk immediately. Conversely, you had better recover all your missing data from it, and then initialize it to make it usable again. Otherwise, the original data will be lost forever. Here, if you don't know how to perfectly recover lost data, you can try using MiniTool Power Data Recovery because of its excellent performance, simple operation and high security.
Hard Drive Not Detected Mac
Related: Solved-Disk Unknown Not Initialized Issue on External Hard Drive
Case 2 – Hard Drive Letter Is Missing
![Old External Hard Drive Not Showing Up Mac Old External Hard Drive Not Showing Up Mac](https://fartinvite.com/pics/imation-apollo-25-portable-hdd-not-recognized-5.jpg)
A drive letter is a single alphabetic character A through Z that has been assigned to a physical drive or drive partition in the computer. And if you want to see your hard drive in My Computer or Windows Explorer, you should assign it with a drive letter. Once the drive letter is missing, you will encounter the 'hard drive not showing up' issue.
Solution
To solve this problem, you can assign a drive letter for it. Windows built –in disk management as well as partitioning software like MiniTool Partition Wizard can help to add a new drive letter on it.
Click here to learn several ways to get missing drive letters back in Windows.
Click here to learn several ways to get missing drive letters back in Windows.
Case 3 – Hard Drive Is Hidden
Now, some users want to turn to third-party software like MiniTool Partition Wizard to hide their hard drive to protect data. However, once accidentally hide a drive containing massive important data, what should we do since this drive isn't showing up in Windows Explorer?
Solution
If drive is hidden by mistake, what should we do since Disk Management only offers Delete Volume feature as well as Help feature, as shown above? Can we delete the hidden volume, and create a new one? Of course, we can! But, this method will cause data loss.
Warning: You had better recover data from the hidden drive before deleting it to create a new one.
Note: Alternatively, you can try using MiniTool Partition Wizard to show hidden hard drive in Windows without losing data because this tool can help you hide/unhide drive conveniently and safely.
Case 4 – Hard Drive Becomes Unallocated
Let's start with a true example:
My external USB 3.0 HD was working perfectly well yesterday. However, today suddenly became an 'unallocated' drive without even a drive name. I'm able to detect the drive but I have no way of accessing it.
The only solution that I've tried so far is to access the HD with another computer. But, the results are the same with those computers. I haven't done anything else..
Here's a screenshot of the problem:
In this case, what should we do? Can we effectively solve this problem without losing original data?
Solution
If your hard disk space turns into unallocated, you are allowed to create new volume on this disk and make it appear in Windows Explorer. However, this solution will cause data loss forever.
In addition, you are highly recommended to recover data from unallocated drive ahead of doing anything else. MiniTool Power Data Recovery is recommended here since this all-in-one tool has been awarded as the top 10 data recovery software on TOPTENREVIEWS.
Case 5 - External hard Drive Is Not Recognized
There's also another situation where the hard drive (especially external hard drive like USB hard drive) is not showing up in My Computer or Windows Explorer. And, you will receive a warning that saying device not recognized.
As a matter of fact, this issue can be caused by various reasons, including the currently loaded USB driver has become unstable or corrupt. For more information about the device not recognized error, please see Error: 'USB Device not recognized' when you try to access a USB external hard drive.
Solution
Here, to fix the 'external hard drive not recognized' error, you can try the below methods.
Method 1: Restart computer
Unplug your USB, restart your computer and plug in and see if it works now.
Method 2: Update device driver
Open Control Panel > Printers and devices. Check if you can see any entry for Unidentified USB device or Unknown Device. Open its Properties and update its driver, if an update is found to be available.
...
Tip: Our previous post USB Flash Drive Not Recognized – Don't Worry Too Much is recommended here to help you get more details about this issue.
Case 6 – Hard Drive Has Wrong File System
Last but not least, if your hard drive is partitioned with the wrong file system, you cannot see it in My Computer or Windows Explorer. For example, you may have formatted the drive with the ext4 file system from Linux or the HFS Plus file system from a Mac. Windows can't read these file systems. But, you can see this drive in Disk Management as shown below:
Solution
To solve this issue, you can delete this drive, and then create a new partition with the newer NTFS file system or older FAT32 file system so Windows will be able to recognize it.
Note: You are strongly suggested to recover data from the drive with wrong file systems at first. Otherwise the original data could be lost forever.
Here, we want to share another case to you.
Sometimes, you will find you cannot access your NTFS drive from another device, such as a DVD player, smart TV, game console, or media center device. This is because that many devices, even Microsoft's own Xbox 360, can't read the Windows NTFS file system. And, they can only access drives formatted with the older FAT32 file system. To fix this problem, simply convert it to FAT32.
After seeing why hard drive isn't showing up in Windows and how to fix this issue, let's move onto the next part.
Recover Data from Hard Drive Not Showing up
From the above description, we can see several factors can cause the hard dive or external hard drive not showing up issue. Although you can fix the 'hard drive not showing up' issue according to the solutions we mentioned above, we advise you to recover data at first. Otherwise, the original data saved on the drive which is not showing up will be lost permanently. However, how?
You are probably wondering:
'How do I effectively recover data from hard drive when it is not showing up?'
Right now, MiniTool Power Data Recovery (PCWORLD, a professional IT magazine, speaks very highly of this data recovery software) can help you effectively recover lost data because of its powerful functions.
Now, let’s see the detailed steps.
Download MiniTool Power Data Recovery Trail edition.
Launch this professional tool to get its main interface as follows.
4 different data recovery modules are listed in the main interface of this all-in-one data recovery software.
- This PC focuses on recovering lost or deleted data from damaged, RAW or formatted partitions. And this module is selected by default.
- Removable Disk Drive is designed to recover lost photos, mp3/mp4 files, and videos from flash drives and memory sticks.
- Hard Disk Drive can recover files after partition loss or deletion.
- CD/DVD Drive helps to recover data from formatted or erased CD/DVD discs.
Here, you can click the Hard Disk Drive to recover lost data. After selecting this module, you will see the following window.
Now, select the target hard drive which is not showing up in Windows Explorer, and then click Scan button. In this window, you are able to click Settings to specify needed file systems as well as file types.
Wait for the full scanning finishes to get the best recovery result.
Finally, select all needed files, and save them. It is recommended to store needed files on another drive. Otherwise, the original data will be overwritten.
The trial edition of MiniTool Power Data Recovery can only scan lost data. If you need to recover more data, please choose the paid edition. Here, you might be interested in this post: MiniTool Power Data Recovery License Comparison.
External Hard Drive Not Recognized Mac
Conclusion
Are you still worried about the 'hard drive not showing up' issue? Now, after reading this post, I guess you might have a basic understanding of how to fix this issue.
Should you have any question or suggestion about the hard drive not showing up in This PC or My Computer, please feel free to send your email to [email protected].
Hard Drive Not Showing up FAQ
- Hard drive is not initialized.
- Hard drive letter is missing.
- Hard drive is hidden.
- Hard drive becomes unallocated.
- Hard drive has a wrong file system.
How do I fix my hard drive not showing up on my computer?
- Initialize hard drive.
- Assign drive letter.
- Hide hard drive.
- Recover hard drive partitions along with data.
- Format hard drive.
How do I get Windows 10 to recognize a new hard drive?
- Right-click This PC.
- Choose Manage.
- Click Disk Management.
- Right-click the new hard drive.
- Choose Initialize Disk to initialize it.
If the drive letter of your USB is missing, drive is out of date, USB drive is damaged, your computer mat cannot recognize your USB drive. You can go to Disk Management to check the status of your USB drive, and then fix this issue.
Summary: About why is external hard drive not showing up on Mac and how to fix this issue to access the external drive on Mac. To prevent unnecessary data loss, you can free download iBoysoft Data Recovery for Mac in macOS Catalina/Mojave/High Sierra and get data off first.
Probably, you connect an external hard drive to Mac but it is not showing up. Don't panic! You can troubleshoot and fix the external hard drive not showing up Mac issue. Don't know where to start? We are here to help.
Take it easy and follow our guide to check the connections, macOS settings, and imperatively, the external hard drive itself. Then, the external hard drive will show up on Mac again.
First of all, let's see why hard drives not working or showing up.
Why is the External Hard Drive Not Showing up on Mac?
Most of the time, Mac not recognizing external hard drives is because of the hard drive corruption and faulty connections. But other factors can make external hard drive invisible on Mac as well.
The causes for external hard drives, USB pen drives, and SD cards not showing up on Mac vary from case to case. Namely, they are:
- The USB cable is broken.
- The USB port is malfunctioned.
- The USB adapter is not working properly.
- The external hard drive is not formatted incorrectly.
- The hardware and software like disk driver need an update.
- The file system of the external hard drive is corrupted.
As a result, you plug the external hard drive into your Mac but nothing happens. It looks like that Mac is not reading your external hard drive. The hard drive won't appear on the desktop or in the Finder. But this doesn't necessarily mean your Mac not recognizing the hard drive. Samsung m3 portable 1tb mac.
It's a definite guide to fix the Mac not recognizing external hard drive issue. It includes why and how to make the external hard drive recognized by macOS again. Read more >>
Guide to Fix External Hard Dive Not Showing up on Mac
Then what do you do if your external hard drive is not detected by Mac? To find and access this external hard drive on your Mac, simply follow our step-by-step guide.
1. Check the Connections of the External Hard Drive
External hard drives like Buffalo Ministation, WD, Samsung, Seagate, and Lacie are connected to Mac using USB cables and ports. But if the connection fails, your external drive won't show up on Mac.
So, if Mac not seeing your external hard drive, check if the external hard drive is properly connected by the following steps.
Step 1: Check the power connections
External hard drive requires electricity to light up, spin, and transfer data. So, if the external hard drive is lack of power, it won't show up on Mac. Microsoft excel for mac 2014. You can do these things to check the power supply.
- 1. For Desktop external hard drives like Seagate Backup plus and WD Elements Desktop, make sure the external hard drive is externally connected to a power socket.
- 2. For portable USB external hard drives, make sure the USB port is not wobbly, dusty, loose, or deformed. If the USB port won't work and can't supply with enough power, you can try another USB port.
If you are working on MacBook, MacBook Air, and MacBook Pro models, two things to notice. Read mac drive on pc free.
- 1. First, make sure your Mac is not in a low power mode. External hard drives can't work if there is no enough power in the USB port.
- 2. Then, make sure the USB hub and USB-C adapter work if your Mac uses Thunderbolt 3 port. Though an authentic USB Type C adapter is better, it lesses problem if you connect the Thunderbolt portable hard drive for Mac directly to your Mac.
Step 2: Check the other connections
Sometimes, the external hard drive like a Seagate hard drive is not recognized by Mac. Then, you need to check the other parts of connections as well, especially when your external hard drive lights on but is not detected or showing up on Mac.
- Check if the wire of the external hard drive is broken.
- Try to connect it to another Mac or even a PC. Possibly, it's just an incompatible USB driver that stops your removable hard drive working.
- Check the USB port on hard drive enclosure case. Sometimes, the external drive is not showing up due to a problematic SATA connection. So if necessary, you can ask help from specialists to open the external hard drive case and have a check.
After checking the connections, you can see if the second hard drive is detected by your Mac.
2. Check Application That's Incompatible with the External Hard Drive
Chances are that some programs are stopping your external hard drive being loaded. Those incompatible programs could be the USB security app, encryption program, or any antivirus software that you installed recently. In this case, you can try to reboot your Mac in Safe mode, which only runs essential macOS items.
- Step 1: Restart your Mac (some Mac computers play a startup sound).
- Step 2: Immediately press and hold the Shift key, and then release the Shift key when you see the progress indicator.
- Step 3:After the restart, reconnect your external hard drive to the Mac and see if it is recognized. If the external hard drive is recognized by macOS in Safe mode, you should start your Mac in normal mode and then uninstall the suspicious programs that you download recently.
3. Check if the Mac is Set to Show Connected External Drives
![Showing Showing](https://s1.yimg.com/lm/ysbp/img/cRER8bLs7z2TUZfHXoBwpbScf_tC8wVxzhtLhH_fXlbRHSLUpg4z5EpHySh7Zqbv.jpg)
Sometimes, the external hard drive is not showing up because your Mac is not set to. If you can't see the external hard drive on Mac, you can get Finder to locate the external hard drive. To make external HDD show up on the desktop and in the Finder of macOS Catalina, Mojave, or earlier, the following steps would be helpful.
- Show the external hard drive on the desktop: Go to Finder > Preferences > General tab and select 'External disks' to make external hard drives show on the desktop.
- Show external hard drives in Finder: Go to Finder > Preferences > Sidebar and make sure the 'External disks' under 'Locations' is ticked. Then your external hard drive will appear in Finder.
4. Access the External Hard Drive by /Volumes/ Folder
If the external hard drive is not showing up on Mac still, where else you can find the hard drive? In fact, you can try your luck by checking the /Volumes/ folder. Most of the time, Mac will show connected and mounted volumes there.
- Step 1:Launch Finder and click Go in the top menu bar > Go to folder.
- Step 2: Then type /Volume/ and hit Enter.
- Step 3: Then you can see the volumes folder that lists all mounted drives and disk images. If your external hard drive is listed, access the hard drive and get to your files there directly.
5. Check Whether the External HDD Can be Found in Disk Utility
To make sure whether your external hard drive is detected by macOS, you can go to Applications > Utilities > Disk Utility and check if Mac is picking up the external hard drive.
Note: If your external fusion drive is not showing up on Mac, you can check if it is recognized as two separate drives by macOS in Disk Utility also.
There are two possible circumstances:
- The external hard drive could be showing up in Disk Utility but greyed out.
- The external hard drive doesn't show up in Disk Utility.
Let's take a look at what we can do if the external hard drive is showing up in Disk Utility.
Step 1: Check if the external hard drive is mounted in Disk Utility
If the external hard drive can be found in Disk Utility, it means that your external hard drive is detected by your Mac. But since you can't see and open your hard drive as usual, we need to confirm more information displayed in Disk Utility.
- 1. Expand the View option and choose Show All Devices.
- 2. Find and select the external hard drive that is not showing up on your Mac.
- 3. Choose Mount at the top menu bar.
You may see no partition showing up in Disk Utility but the manufacturer's name like WD and Seagate. This means the partition table (A unit of data describing the partition information on the hard disk) is damaged or lost. As a result, macOS is unable to recognize the external hard drive. In this situation, you're advised to recover important data with iBoysoft Data Recovery for Mac first, and then reformat this hard drive.
Step 2: Check if the file system of the external hard drive is recognizable
The file system manages how and where data on a storage disk is stored, accessed and managed. So it's crucial to make sure that the file system is not corrupted and it is doing a good job.
To check the file system in Disk Utility: simply select the drive you want to check, and then the disk information, including file system and storage capacity, would be displayed at right.
You could see one of the 4 possible circumstances:
First: The file system of the external HDD is corrupted
The file system could be damaged due to improper ejection or bad sectors. As a result, the disk information is not displayed correctly. And you are unable to mount this external hard drive on Mac. To repair this corrupted external hard drive, First Aid on your Mac is a great disk repair tool to use.
- 1. Launch Disk Utility.
- 2. Choose the grayed out external hard drive from the left sidebar.
- 3. Click the First Aid button on the top and then choose Run to confirm this operation.
If Mac is unable to recognize the external hard drive still or First Aid failed to repair the external hard drive, the file system or some core data is too corrupted to be repaired by First Aid. Here are some error reports you might receive from Disk Utility:
In this case, you have to reformat it to assign a new file system to this hard drive. However, as it was pointed out before, reformatting will clean the external hard drive and erase your data on this drive. If you don't have any backup and don't want to lose the data, you are advised to recover files from the corrupted external hard drive with iBoysoft Data Recovery for Mac.
iBoysoft Data Recovery for Mac is powerful in hard drive data recovery, especially when your Macintosh hard drive or external hard drive is not recognized on Mac. It helps you recover lost data from unreadable, unmountable, corrupted, and formatted drives. Except for hard drives, this data recovery software also works with USB flash drives, memory cards, SD cards, pen drives, CF cards, etc.
To recover lost data and reformat the corrupted external hard drive:
- 1.Download and install iBoysoft Data Recovery for Mac on Mac.
- When external hard drive is not showing up normally on Mac due to disk corruption, the data on the drive becomes a great concern. To recover and access your files on the unrecognized external hard drive, iBoysoft Data Recovery for Mac is a handy tool to help.
- 2. Scan for lost data on the external hard drive.
- After launching this program, check if you can see the unrecognizable/corrupted external hard drive is listed in the main interface. If you can see it, click on Scan to search for your files on this external hard drive. If not, you need to send it to data recovery lab.
- 3. Preview the searching results, choose files you need, and click Recover to get them back.
- When you can't open the external hard drive and access files normally on your Mac, you can use the Preview feature of iBoysoft Data Recovery for Mac to see your files. It helps to make sure that your documents, photos, music files, videos, and emails are in good condition.
- 4. Launch Disk Utility and locate the external hard drive from the left sidebar of the window.
- 5. Select this unrecognizable external hard drive and click the Erase button.
- 6. Complete the related information (name, format, scheme), then click Erase to reformat the problematic external hard drives in Disk Utility.
Second: The external HDD is APFS formatted
If your Mac uses macOS 10.12 or earlier but external hard drive is APFS formatted, you are advised to update your macOS so that it can work with the latest file systems, software, as well as some firmware relating to USB peripherals and devices.
To update macOS, you can:
- 1. Right-click the Apple logo at top right, and then choose System Preferences.
- 2. Find and open Software Update to check for new macOS update.
- 3. Back up your important files and follow the wizard to update your operating system.
Third: The external hard drive is Read-only Windows NTFS formatted
Even though Mac can recognize NTFS drive, you can only read NTFS without write permission. And some times, the external hard drive will not work properly. In this case, do not force the external HDD to mount in read-write mode with 'LABEL=NAME none ntfs rw,auto,nobrowse' in Terminal. Changing 'fstab' is risky and unstable.
Instead, you have two other options:
- If you need to use this NTFS external hard drive both for Mac and PC, you can install an NTFS for Mac program to fix this issue without reformatting.
- If the external hard drive is used only for Mac, you can back up your important files and then reformat it to a compatible file system like HFS, FAT32 or exFAT.
Fourth: The external hard drive is formatted with unrecognizable file system
Mac can't recognize non-native file systems. So, other file systems like Linux EXT3 and EXT4 would not be readable by Mac. In this case, the only solution is to reformat it to make it compatible with your Mac.
Warning: Any operation relating to 'Erase' and 'Format' would wipe files off your storage devices. So make sure you have a copy of the data, or you can recover files from this external hard drive with iBoysoft Data Recovery for Mac.
The solutions above are prepared for external hard drive showing up in Disk Utility on Mac.
6. Check and Fix Hardware Information of the External Hard Drive
Nevertheless, what if the external hard drive is not showing up in Disk Utility at all? It should be some hardware problems that stop the external hard drive showing up on Mac. Don't worry! You can check and repair those problems with the following solutions.
Step 1: Find invisible external hard drive in System Information
If the external hard drive doesn't show up in Disk Utility, you can check if the Mac has detected and recognized its hardware information in System Information: Go to Applications > Utilities > System Information > USB, and then check the external hard drive information.
If you see the external hard drive showing up there but not in Disk Utility, the hard drive may be under repair by macOS. Go and check it the Activity Monitor.
- 1. Click the Launchpad and find the Other folder. Find and open Activity Monitor there.
- 2. Type and search if there is any process named 'fsck_hfs' or something similar. (If your external hard drive is exFAT formatted, then it should be 'fsck_exfat'.)
- 3. Select that task and click the Force a process to quit button at the upper left to stop it. and Then the external hard drive should show up on the desktop of your Mac.
If the parameters of the external hard drive are not recognized correctly or even not recognized, you can move forward.
Hard Drive Connected But Not Showing Up
Step 2: Reset your Mac's NVRAM
NVRAM is helpful to retain the information while power is turned off. If you experience issues related to these settings or others, resetting NVRAM might be helpful to get your Mac to recognize the external hard drive.
- 1. Shut down or reboot your Mac.
- 2. Immediately press these four keys in a sequence: Command + Option + P + R.
- 3. Hold the keys for at least 20 seconds and after you hear the second chime, release the buttons.
- 4. After releasing the keys, your Mac will restart and hopefully your drive will show up.
External Hard Drive Won't Show Up Mac
Step 3: Reset the SMC on your Mac
In certain circumstances, resetting SMC can be a solution because SMC is responsible for lower-level functions like power and hardware.
Note: The method of resetting SMC is varied from models to models, so check and know how to reset the System Management Controller (SMC) on your Mac.
Let's take resetting SMC of a MacBook Air, MacBook Pro Retina, or MacBook Pro's with an internal non-removable battery as an example:
- 1. Shut down your MacBook Air/MacBook Pro.
- 2. Connect the power adapter to the Mac.
- 3. After your Mac shuts down, press Shift + Control + Option on the left side of the built-in keyboard, then press the power button at the same time. Hold these keys and the power button for 10 seconds.
- 4. Release all keys and the power button at the same time. Then press the power button again to turn on your Mac, which would take a little time.
Step 4: Run Mac diagnostics to detect hardware issues
Apple Service Diagnostic is a set of diagnostic tools used by technicians to find faults. You can use it to confirm or deny your suspicions. If the external hard drive has been physically damaged, you have to send it to local disk repair center.
- 1. It is advised to disconnect all the external devices except keyboard, mouse and other useful devices.
- 2. Reboot your Mac or you can power on your Mac if it powers off.
- 3. Press and hold D button on your keyboard. Hold the button until you would be asked to choose the language.
- 4. After selecting your language, it will display a progress bar stating Checking your mac.
- 5. After completing the diagnostics, it will suggest you the solutions for the errors diagnosed.
To sum up
It's relatively complicated to check out why is an external hard drive not showing up/recognized/detected by macOS. If you worry about data loss in this process, you can recover all important data from the external hard drive first with the assistance of iBoysoft Data Recovery for Mac.
Moreover, to prevent an external hard drive not showing up issue, it's advised to properly eject or connect your external drives at any time. Besides, always backing up critical files on another drive or in the cloud would help a lot.