Have you plugged in an external hard drive, USB flash drive or other external storage device and got the message “The disk you inserted was not readable by this computer”? Don’t worry, we’re here to help!
Errors like this can have a logical or a physical cause, and repeated repair attempts can make things worse. If the files matter, see how professional data recovery works, starting with a free diagnosis.
The message doesn’t say what caused the problem, but there are a few basic steps you can try to fix it without putting the data on your device at risk.
Read on to find out what this error means on macOS, Apple’s operating system, and how to fix it.
What does “The disk you inserted was not readable by this computer” mean?
This error appears when, for some reason, your Mac can’t read the data on a hard drive (external drive) or USB flash drive. There can be several causes, most often a problem with the device itself.
The error can also be caused by the operating system, for example outdated software or drivers. In these cases, finding and fixing the problem in macOS may be enough. Always keep your system and drivers up to date to avoid errors like this.
When the problem lies with the device itself, these are some of the possible reasons your Mac can’t read it:
Drive failure
Devices fail from time to time, especially when they are old and worn. The drive may have mechanical damage, or its USB connector may be worn after being plugged in and out many times.
Corrupted file system or partition table
Drives can use different file systems, and not every operating system supports all of them.
In addition, the operating system has to read the drive’s partition table to know how the data on it is organized. If this information is corrupted, the computer won’t be able to read the data.
A new drive
A brand-new drive may have no partition information yet, which triggers the same error. These are known as “uninitialized” drives.
Virus attacks
Malware can overwrite the drive’s data structures and make it unreadable to the operating system.
How to fix “The disk you inserted was not readable by this computer”
There are several ways to fix this error, depending on what’s causing it. If the drive clicks or makes unusual noises, skip the steps below and go straight to a specialist. Otherwise, here’s what you can try:
1. Try another USB port
If the port is damaged, plugging the drive into another one may solve the problem. If it doesn’t, try a different USB cable too, as the cable could be the culprit.
If the Mac’s USB ports turn out to be the problem, restart the Mac; on Intel-based Macs, you can also try resetting the SMC.
2. Check the file system
To work normally, a drive’s file system has to be supported by the operating system. macOS reads and writes APFS, Mac OS Extended (HFS+), exFAT and FAT32. Drives formatted as NTFS (the usual Windows format) can be read, but macOS can’t write to them without additional software. If the drive uses a format the Mac doesn’t support, you’ll need to reformat it to one of those systems — exFAT is the best choice if you also use it with Windows.
However, formatting the drive erases its data. If you need that data, copy it to another drive first, using a computer that can read the current format (for example, a Windows PC for an NTFS drive).
3. Check and repair the unreadable drive (flash drive, SD card)
macOS has a built-in tool for checking and repairing disk errors, especially file system errors. First Aid writes to the drive, so if the data is important and the drive is failing, have it recovered before you run it. To use it, follow these steps:
- In “Applications”, open “Utilities”;
- Open “Disk Utility”;
- With the device connected to your Mac, select the unreadable drive in the sidebar;
- Click the “First Aid” button at the top of the Disk Utility window;
- When asked whether you want to run First Aid, click “Run”;
- The check will start and may take a few minutes, looking for problems and trying to repair them;
- When it’s finished, click “Done” and eject the drive safely;
- Plug the drive back into your Mac.
4. Initialize (erase) the drive — only if you don’t need the data
A new drive needs a partition scheme before the operating system can use it. This information is stored in a partition table — the “Master Boot Record” (MBR) on older drives, or the GUID Partition Table (GPT) used by macOS today.
On older drives that have been in use, the partition table may become corrupted and block access to the drive. Creating a new one is called “initialization”.
Initializing a drive erases it: a new, empty partition table and file system are created, and the existing data is no longer accessible. So only do this if you already have a backup of your data or don’t need it. If the files matter, recover them first.
To initialize the drive, follow these steps:
- Open Disk Utility;
- Select the unreadable drive in the sidebar;
- Click the “Erase” button at the top of the Disk Utility window;
- Give the drive a name, choose the format and scheme you want, and click “Erase”.
This erases the drive and creates a new file system that the Mac can read — but the drive will be empty.
If you’ve formatted a drive and need the files back, read our article on 11 ways to recover a formatted disk.
What if I still can’t access the data on the drive?
There are various ways of trying to regain access to a drive, but they don’t always work. If they don’t, avoid trying procedure after procedure, which can cause further damage to the device. This is the time to get professional help.
A professional can identify other problems the device may have and use advanced techniques to recover the data on it.
Bot specializes in data recovery, with more than two decades of experience, more than 200,000 cases and a 96% success rate. It has reception points in Lisbon, Coimbra, Porto and Braga and uses specialized methods and equipment for cases like this.
If you need help, fill in this form and Bot will get in touch.
How do I access my Mac’s drives?
If you use macOS and want to check the details of your drives, it’s simple. As explained by Apple Support, Disk Utility lets you check and repair errors, format and manage volumes on storage devices, and troubleshoot disk problems.
There are two ways to open it:
- Open Launchpad, type “Disk Utility” in the search field and click the icon;
- In Finder, choose “Go” > “Utilities” and double-click “Disk Utility”.
An overview of the “not readable” error on a Mac
There’s no complicated explanation for this error. It usually appears when you connect a storage device to a computer running macOS.
But don’t panic — it doesn’t happen every time. The message usually means that the device, or the data on it, has a problem that prevents the system from reading it properly.
What makes a drive unreadable on a Mac
As mentioned above, there are many possible causes, so it’s not always possible to know exactly why a drive can’t be read. The main ones are:
- Drive failure
- Corrupted file system or partition table
- A new drive
- Virus attack.
Read next
Conclusion
Not being able to read a drive on a Mac is certainly frustrating. The good news is that there are solutions that often work.
And if you still can’t access your device after trying them, don’t worry — Bot Data Recovery can help. We have more than two decades of experience and specialize in professional data recovery.
Don’t lose your data to everyday problems. Contact us with any questions — our team of experts is ready to help.
