USB drive asking to be formatted?
Don't click—your data is most likely still there
Windows says "You need to format the disk in drive X: before you can use it," and your Mac says "The disk you attached was not readable by this computer." Often only the file system's records are damaged, and the files themselves are still on the drive. Once you format it, getting them back is much harder. Follow the steps below to check, read-only on your Mac, whether your files are still there.
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What not to do first
Don't click "Format" or "Initialize"
Formatting writes a new file system over the old directory records. When the prompt appears, click "Cancel" on Windows or "Ignore" on a Mac.
Don't run a repair first
chkdsk /f and Disk Utility's First Aid both write to the disk. If a repair fails, files that were still readable can be lost too. Get your files out first, then think about repairing.
Don't keep replugging it
Every time you plug it in, the system tries to read and fix it. Plug it in once, then scan read-only.
Stop if it isn't detected at all
If it doesn't show up anywhere, or its capacity shows as 0 or very small, the drive's controller has most likely failed. Software can't fix that; take it to a professional data recovery service.
Common causes, and what can be done today
| Recoverable | Notes | |
|---|---|---|
| Unplugged without ejecting, or power lost while unplugging | ✓ | File system records weren't fully written; opened read-only with progressively more lenient checks |
| A format the Mac doesn't recognize (Ext4, XFS, Btrfs) | ✓ | Not actually damaged; macOS just can't read it |
| BitLocker-encrypted USB drive | ✓ | Opened read-only after you enter the password or recovery key |
| USB drive has bad blocks and reads very slowly | ✓ | Image it first, then find files in the image |
| Already formatted | Not yet supported | Needs a deep scan |
| Partition gone, shown as "Unallocated" | Not yet supported | Needs a deep scan |
| Not detected at all, or capacity shows 0 | — | Usually a controller failure; take it to a professional |
Not sure which case applies? Scan with the free version first: volumes that can be opened are listed right away, and you can preview files for free.
Read a USB drive that asks to be formatted on a Mac with NAS Rescue
It has NAS in the name, but it works just as well on a single USB stick, external drive, or SD card: connect it, scan, preview for free, and recover once you see your files. You'll also need another disk with enough free space for the recovered files.
- 1
Plug in the USB drive
When you see "The disk you attached was not readable by this computer," click "Ignore." Don't initialize it.
- 2
Select disks
Open NAS Rescue and select the USB drive in the disk list. If it reads very slowly, turn on "Check disk health first"; it will tell you whether to image the drive first.
- 3
Scan and preview
Click "Scan Disks." It opens the volumes on the USB drive read-only, and if mounting fails, it automatically retries with a more lenient read-only method. It never repairs or writes anything. Then browse the folders and open photos, videos and documents for free to confirm the files you need are there.
- 4
Recovery
After upgrading to Pro, copy the files to another disk with modification dates preserved, each one verified with SHA-256. Once your files are safe, format the USB drive and keep using it.
Q&A
My USB drive says it needs to be formatted. Can the data be recovered?
Usually, yes. A format prompt usually means the file system's records are damaged or the computer doesn't recognize the format; the file contents are still there. As long as you haven't formatted it, scan read-only first, and in most cases you'll see your files.
My USB drive asks to be formatted, but formatting fails. What now?
That often means the drive has bad blocks, or its controller has switched to write protection. Stop trying to format it. Scan it read-only with NAS Rescue and copy out whatever files can be read; if it reads very slowly, image it first.
I already formatted it. Can I still get my files back?
Not with NAS Rescue yet. After a quick format, old files can only be found with a "deep scan," which isn't supported yet. Until then, don't write any new files to the drive.
Can I fix it with Disk Utility's First Aid or chkdsk?
Wait until your files are out. A repair rewrites the directory records on the disk, and if it fails, files that were readable may be lost too.
Why use "NAS Rescue" for a USB drive?
Its engine already opens NTFS, exFAT, FAT32, Ext4, XFS, Btrfs, and other formats read-only, tries progressively more lenient mount methods, and can image failing drives—all of which works just as well for a single USB drive.
Can it recover a Mac-formatted APFS USB drive?
APFS isn't supported yet. For Mac-formatted drives, check them in Disk Utility first.
Related products and guides
CrossDriver NAS Rescue
Connect USB sticks, external drives, SD cards, and NAS drives to a Mac, scan read-only, and preview for free before recovering.
External hard drive not reading on Mac
When an external drive won't read on a Mac, troubleshoot step by step, by symptom.
Mac external drive is read-only
Opens but read-only? It's most likely NTFS.
If you haven't formatted it, your files still have a chance
Download NAS Rescue and check for free whether the files on your USB drive are still there.
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