The disk you inserted is not readable by this computer - macOS error. What should I do?

[Frogivers]

Hi everyone, I’ve run into an issue and I’m hoping someone here can help.

 

Here’s the situation: I have a 4TB WD external drive that I’ve been using for years with my Windows PC. It mainly holds photos, videos, and backups of some old work files. A couple of days ago, I tried connecting it to my new MacBook, which I now use for work, to sort through some of those files and transfer what I need.

 

But as soon as I plugged it in, I got the message: “The disk you inserted is not readable by this computer.” The options given are Initialize, Ignore, and Eject. Naturally, I clicked Ignore - I didn’t want to risk messing anything up.

 

The disk doesn’t show up in Finder, but I can see it in Disk Utility. However, the Partition Map is listed as Unknown, and the File System is also Unknown.

 

Has anyone come across this before? Is there any way to access the files without formatting the drive? From what I understand, that’s exactly what the Mac wants me to do - but I’d rather not lose everything on the disk.

 

✅ UPD: I backed up my disk and restored all my files from that copy with Disk Drill, it's awesome.

Edited August 14, 2025 by Frogivers

[UrbanExplorer7]

Hey, yeah this kinda thing happens a lot with Macs when you try plugging in a drive that was on Windows before - especially if it’s an older one or the file system’s just a bit borked.
Quick q though: do you know what file system it was using? Like NTFS, exFAT, or… some mystery format from the Windows XP era?
Also, did you ever use it on Windows with any funky tools like Paragon, Veracrypt, or whatever? Some of those write weird stuff to the drive that macOS just looks at and goes “nah fam, not touching that,” hence the unreadable disk error.
But yeah, props for not hitting “Initialize.” That’s basically Apple’s polite way of saying “wanna nuke this thing?” so dodged a bullet there. As long as you didn’t click that, there’s still a decent shot at reviving the partition and pulling the data off.

[Frogivers]

@UrbanExplorer7, thanks for the reply! To be honest, I’m not exactly sure what file system is on the drive, but most likely it’s NTFS. I didn’t use any special tools when writing to it - just copied files manually through standard Windows Explorer.

[TechieGuru99]

If the drive is formatted as NTFS, macOS should still be able to read it - at least in read-only mode. Apple introduced native NTFS support back in the 2000s, while Microsoft, ironically, never offered proper support for HFS.

 

However, if Disk Utility shows the file system as ‘Unknown,’ it likely points to an issue with the partition itself or possibly a hardware problem with the drive.

 

The first step I’d suggest is reconnecting the disk to your Windows PC. If it opens there without issues, back up the data immediately - either to another drive or by transferring it to your Mac via network sharing.

 

But if Windows also fails to read it or prompts you to format the disk, then it’s a more serious problem. At that point, you’ll need to take some recovery steps to retrieve the data.

[Frogivers]

I tried reconnecting the drive to my Windows PC, but unfortunately, it gives me a similar message - it asks to format the disk, It’s just worded differently than on my Mac, where I got ”The disk you inserted was not readable by this computer” 😭

[UrbanExplorer7]

Alright, so here’s the deal  -  it’s either your file system is messed up (corruption and all that fun stuff) or the disk has bad physical sectors. But hey, silver lining: there’s still a decent shot you can get your data back.

 

Here’s what I’d do: First thing, make a byte-by-byte clone of the drive. Like, don’t skip this. Use whatever tool you want but I’d recommend Disk Drill  -  they actually updated their backup feature in version 6 and it’s supposedly way gentler with failing disks. Kinda important if the drive is already halfway to the grave. And yeah, this is kinda the golden rule before ANY recovery attempt, especially when the disk itself is dodgy, not just “oops I deleted a file.”

 

Disk Drill can both clone and recover, so win-win. Plus, if your drive is still showing up in Disk Management (even if it’s just the size and not the partitions), you’re still in the game.
Once you’ve got the clone, unplug the OG drive and toss it back on the shelf  -  you’re done abusing it. Then scan the backup instead, either with Disk Drill or whatever else that can read from clones. The software’s gonna dig for whatever scraps of the file system it can find, and if that fails, it’ll scan for known file signatures. Some tools will also try to find lost partitions, each app calls these scans different fancy names, but it’s all the same idea. Bonus: you can scan the backup as many times as you want without risking the actual disk, which is kinda the point.

 

If you don’t wanna pay for software, you can give TestDisk a shot  -  just a heads up, it’s all text-based and not exactly user-friendly unless you’ve got some patience (or Google-fu). There’s guides tho, even on their forums. Just PLEASE only mess with TestDisk after you’ve got that backup. Write the wrong thing directly to the drive and congrats, you’ve just made your data extra unrecoverable.

 

Worst case  -  if you see a ton of red blocks (bad sectors) while cloning in Disk Drill, just stop and take it to a data recovery service. That’s hardware level stuff and you don’t wanna mess with it unless you enjoy bricking drives for sport
 

Edited August 14, 2025 by UrbanExplorer7

[D_Harris_05]

I agree with the previous response - it explained everything perfectly. I’ll just add that I’m personally very satisfied with Disk Drill and would wholeheartedly recommend it. Plus, once you’ve created a backup, you can safely experiment with different recovery tools without risking the original disk. Just keep in mind that scanning a full hard drive backup can take quite a while, especially if the drive is large - so you’ll need to be patient if you go that route

[Frogivers]

I’ve already downloaded Disk Drill and I’m currently creating a backup of the disk.

 

I’m copying everything to a friend’s SSD to speed things up, though it looks like the slow speed is on my HDD’s side.

 

P.S. So far, I haven’t seen any red blocks - fingers crossed it stays that way!

[D_Harris_05]

Well done - it’s great that you stuck with the backup strategy 👍
By the way, I just remembered: it’s actually better to create a copy in Recovery Mode. That way, the system won’t interact with the disk in parallel during the process. But if everything’s running smoothly on your end, there’s no need to interrupt anything - just a heads-up for future reference

[Frogivers]

Thank you! The copying is going well so far, but it’s definitely slow - about 800GB copied in 4 hours, and I’ve still got 4TB total…
Also, some bad blocks have started to appear, unfortunately

[UrbanExplorer7]

Well get ready to be patient  -  if the disk’s got bad sectors, the whole process is gonna be sloooow. Like, go make yourself a coffee and binge some YouTube slow.
But the good news is Disk Drill handles it pretty well. If the drive decides to nope out mid-process, it’ll just pick up where it left off when you restart it. So honestly, just kick it off, go live your life, and check back later. No point in babysitting it unless you enjoy staring at progress bars for hours

[Frogivers]

Alright, I finally finished backuping!
I ran a scan with Disk Drill, and it’s already found a bunch of photos, videos and documents - even though the scan has just started. I can tell these are definitely my photos and videos - woohoo!
It’s still estimating a couple more hours to complete the scan, though

[TechieGuru99]

7 minutes ago, Frogivers said:

Alright, I finally finished backuping!
I ran a scan with Disk Drill, and it’s already found a bunch of photos, videos and documents - even though the scan has just started. I can tell these are definitely my photos and videos - woohoo!
It’s still estimating a couple more hours to complete the scan, though

Congratulations, my friend! Just a quick reminder - make sure to check all your recovered files. Some might be damaged, especially if parts of the data were stored in bad sectors. That said, most files should have come through intact

[Frogivers]

I ended up buying the PRO version to recover the files, since most of what I tested in preview worked and looked intact. After recovery, I checked everything - most of the files were fully recovered and working.
Thank you so much to everyone who helped out! Honestly, I thought it was over and I’d have to say goodbye to both the drive and the data on it