The disk you inserted was not readable by this computer error. Help?

[degras19]

I'm new here, hope this is righ place to post. Ran into something weird today and I’m hoping someone here knows whats up.
I plugged in an external hard drive, and right away I got a popup that says The disk you inserted was not readable by this computer. It’s an old 1TB Samsung ExFAT drive that used to work just fine. Tried it on my MacBook Pro (Sonoma), and no dice. Same cable I’ve always used. I also tried switching ports, rebooting… nada.
What’s the move here? I really don’t want to format it, there’s stuff on there I don’t have backed up. Any help appreciated.

 

[Update]
Here’s what ended up working for me:

Got the files off with Disk Drill, then erased the drive and reformatted it in APFS. That error is gone now and it seems to be working fine again.

Appreciate the help from everyone here!!!

 

Edited July 18, 2025 by degras19

[tadoka]

exFAT is kinda sketchy on Macs. It works in theory, but I’ve seen people get “the disk you attached was not readable by this computer” message when using exFAT drives (especially if they were used back and forth Windows<>macOS all the time).
If I were you, I’d try plugging the drive into a Windows PC first. If Windows recognizes it, back up everything right away.Then once you’ve got the data, plug it back into your Mac and reformat it to APFS ( Mac-only use) or exFAT again if you really really need that cross-platform, but just know it’s a bit of a gamble long-term.

[TechieGuru99]

Hey @degras19 have you tried opening Disk Utility and running First Aid on the drive?
Sometimes macOS just has trouble mounting a drive due to file system issues, and First Aid can patch things up enough to get it working. Just launch Disk Utility from Applications, select the external drive from the sidebar (top-level device, not just a volume), and click First Aid at the top.

 

[UrbanExplorer7]

@tadoka hold up, disagree with you on this one. EXFAT isn’t the problem here. macOS supports it natively and has for years. I use exFAT drives all the time for sharing files, and I’ve never had issues. The idea about trying it on a Windows PC isn’t bad though, who knows, maybe it’ll read fine there and you can back stuff up.
Also @degras19 did you check Disk Utility? What exactly does it show?

 

[Oyecomova]

13 minutes ago, UrbanExplorer7 said:

@tadoka hold up, disagree with you on this one. EXFAT isn’t the problem here. macOS supports it natively and has for years. I use exFAT drives all the time for sharing files, and I’ve never had issues. The idea about trying it on a Windows PC isn’t bad though, who knows, maybe it’ll read fine there and you can back stuff up.
Also @degras19 did you check Disk Utility? What exactly does it show?

 

.. that's true.. exFat is compatible with Windows and Linux.. and the one that has the highest data transmission rates is macOS..

[D_Harris_05]

In my experience, when you're trying to fix disk not readable on a Mac, it usually comes down to a few common things.

• First thing I always check is the cable. I know it sounds basic, but I’ve had drives throw errors just because the USB cable was acting up.
• Then there’s the unsupported file system. I saw you said it was exFAT, but still I’d double-check just to make sure. 

 

[degras19]

Also quick question I saw people mention resetting PRAM/NVRAM online. Does anyone actually know if that helps with issues like this?

 

[D_Harris_05]

Just now, degras19 said:

Also quick question I saw people mention resetting PRAM/NVRAM online. Does anyone actually know if that helps with issues like this?

 

It depends. Do you have an older Mac with Intel or Apple Silicon (like M1- M4)? If it’s an Intel Mac, then yeah resetting PRAM/NVRAM can sometimes help with glitches, including issues like USB drives not mounting or your MacBook throwing the disk you attached was not readable message. It doesn’t hurt anything, so worth a try.
But Apple Silicon machines don’t use PRAM/NVRAM the same way, and you can’t manually reset it with the old key combo, it’s reset automatically whenever you do a full shutdown and start the Mac up cold. So basically, a normal restart already does it.

 

[degras19]

@D_Harris_05 Thanks for the explanation.I’m on an M2 Mac, so sounds like the reset stuff doesn’t really apply.

Checked Disk Utility just now. It shows the drive under “External” just the device name, no volume under it. No Mount button. First Aid is grayed out too. So macOS sees something,. but that same disk not readable by this computer popup comes up. 
Haven’t tried it on a Windows PC yet. Might do that later today, just need to pop over to my neighbor, hes a Windows guy. but maaan it's a bummer i have really important docs on it.

 

[PixelDreamer5]

Just throwing this out there I got the “The disk you inserted was not readable by this computer” message a while back when I tried to open a drive that had been used with Linux (EXT4 I think)

 

[UrbanExplorer7]

18 minutes ago, degras19 said:

@D_Harris_05 Thanks for the explanation.I’m on an M2 Mac, so sounds like the reset stuff doesn’t really apply.

Checked Disk Utility just now. It shows the drive under “External” just the device name, no volume under it. No Mount button. First Aid is grayed out too. So macOS sees something,. but that same disk not readable by this computer popup comes up. 
Haven’t tried it on a Windows PC yet. Might do that later today, just need to pop over to my neighbor, hes a Windows guy. but maaan it's a bummer i have really important docs on it.

 

Since the disk shows up in Disk Utility but has no volume, you’ve got two options right now, don’t format it just yet.
You can either run a data recovery tool directly on the disk to try and pull files off it,  or even better create a full disk image (basically a clone of the drive) and scan that instead. If the drive itself is starting to go bad, scanning the image is way gentler. Saves you wear-and-tear on the actual disk. II’ve done this a couple times before personally used Disk Drill and had good luck with it. It has a solid disk imaging feature built in (Byte-toByte backup), and you can use that part for free (you'll need the Pro version to actually recover files from the image though)
Also might be worth checking the SMART on the drive, Disk Drill can show that too (under Extra Tools). Could give you a heads-up if the disk is physically failing. That  disk you attached was not readable… message doesn’t always mean the drive is on its last legs, but if you’ve got important stuff on there, better safe than sorry.

 

Edited July 17, 2025 by UrbanExplorer7

[Kelso]

2 hours ago, degras19 said:

I'm new here, hope this is righ place to post. Ran into something weird today and I’m hoping someone here knows whats up.
I plugged in an external hard drive, and right away I got a popup that says The disk you inserted was not readable by this computer. It’s an old 1TB Samsung ExFAT drive that used to work just fine. Tried it on my MacBook Pro (Sonoma), and no dice. Same cable I’ve always used. I also tried switching ports, rebooting… nada.
What’s the move here? I really don’t want to format it, there’s stuff on there I don’t have backed up. Any help appreciated.

Yoi can try to restart into Safe Mode (https://www.wikihow.com/Start-Your-Mac-in-Safe-Mode). Try holding Shift when you reboot your Mac it forces a Safe Boot. Sometimes weird stuff like that helps when you’re getting errors like disk not readable by this computer on Mac. Maybe yours just needs a little reset to recognize the drive.

 

[UrbanExplorer7]

@Kelso Safe Mode won’t really change anything. This isn’t a software conflict or a startup issue it’s a case where the Mac CAN see the physical disk but not the file system / partition structure. That’s why it shows the disk you inserted was not readable message. It’s a file system level problem. Booting into Safe Mode might help with other USB-related weirdness, but not here. 

[TechieGuru99]

If you’ve got important stuff on that drive, I totally agree with @UrbanExplorer7 it’s smart to try a data recovery app first before doing anything that might wipe it.
Just to throw a few options out there: PhotoRec, EaseUS, Disk Drill, Cisdem. PhotoRec is totally free one. It’s a Terminal-based tool though, so not point-and-click. It recovers files based on their signatures, which means it won’t preserve folder structure or original file names.
After that (assuming the drive is physically ok) you should be able to just Erase it in Disk Utility, pick your format (APFS or exFAT), and it should be good to go again.
By the way, just curious is there a reason you're using exFAT? Do you use this drive with non-Mac computers too? Okay if you do, but if it’s just for your Mac, APFS is usually better optimized.

 

[degras19]

@TechieGuru99Thanks for all the suggestions ,super helpful. I mostly use this drive only with my Mac. So I don’t really know why I went with that format in the first place.

 

[degras19]

@UrbanExplorer7 so I downloaded Disk Drill like you suggested. Checked the SMART it shows two drives, Apple SSD and the 1TB Samsung one. Only thing is it only show info for the Apple SSD. The external one just shows up in the list, but no stats or health info. Not sure if that means it has big problems 💀
I saw that Byte backup option in the app, that’s the one you meant by creating a disk image, right? Just wanted to double-check before I run it. Is it safe to use on a drive that’s acting weird like this? And once it’s done, how do I scan that image?

 

[UrbanExplorer7]

4 minutes ago, degras19 said:

@UrbanExplorer7 so I downloaded Disk Drill like you suggested. Checked the SMART it shows two drives, Apple SSD and the 1TB Samsung one. Only thing is it only show info for the Apple SSD. The external one just shows up in the list, but no stats or health info. Not sure if that means it has big problems 💀
I saw that Byte backup option in the app, that’s the one you meant by creating a disk image, right? Just wanted to double-check before I run it. Is it safe to use on a drive that’s acting weird like this? And once it’s done, how do I scan that image?

 

Look closely there’s usually a little button that says something like “Enable SMART for external drives” . If your enclosure supports it, that might pull the extra health info in. 
And to answer your earlier question, the Byte-to-Byte backup is safe to use. All it does is create a full image of the drive as it exists right now. So no matter what happens to the physical drive later you’ve got a frozen copy of everything that was still there at the time: visible files, hidden stuff, even deleted files that haven’t been overwritten yet. Like a carbon copy of your full disk, bit for bit.
Once the image is done, just go back to main menu and click “Attach disk image”, select the file you made, and run your scan on that instead of the real drive. It’s safer and puts zero extra strain on the hardware.

 

[degras19]

Hey again, just wanted to follow up. I did everything you said @UrbanExplorer7
went ahead and made the BytetoByte backup. Then my neighbor showed up, so I figured might as well try it on his Windows just to rule that out .But nope, same story there. wouldn’t open. So I went back home, scanned the image like you suggested pulled around 50GB of important files off of it: personal stuff, work folders. The rest was random junk I didn’t care about so I let it go. Then I erased the drive in Disk Utility, formatted it to APFS, and now it mounts fine. No more fix disk not readable on Mac  or anything. So far so good.
Also found that Enable SMART button and it started showing proper health info for the Samsung drive. Says everything’s good. Kinda weird though it shows everything’s fine, so I don’t really know what caused it in the first place.
Either way, really appreciate all the help from everyone here. Peace 🙌