External hard drive not reading on your Mac?
First, figure out which case it is
"Not reading" can mean a cable or power problem, a format the Mac doesn't support, a damaged file system, or bad sectors. Take a minute to work out which one it is, then fix that. Don't rush to format.
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Start by checking Disk Utility
Open Applications › Utilities › Disk Utility, choose View › Show All Devices in the top-left corner, and see whether the drive appears in the sidebar.
- 1
Not in the list
Try another cable and another USB port, and connect directly instead of through a dock or hub. If a 2.5-inch drive isn't getting enough power, use a powered Y-cable or enclosure. Still nothing? See "not detected at all" below.
- 2
Listed, but the volume is grayed out
The drive itself connects; the problem is the volume: an unsupported format, an unclean shutdown, or a damaged file system. Use the table below to find the fix.
- 3
Listed, but extremely slow or freezing
Copies fail partway, Finder spins, or the drive keeps disconnecting: most likely bad sectors. Stop reading it over and over, and image it first.
Common situations and fixes
| Why | Fix | |
|---|---|---|
| Shows in Finder, but read-only | NTFS, which macOS can only read | Read and write with CrossDriver NTFS |
| "Not readable by this computer," and the disk came from Linux or a NAS | Ext4, XFS, or Btrfs, which macOS doesn't support | Open with All in One or the matching single-format app |
| Used on Windows, reported as not shut down properly | Windows Fast Startup, or unplugged without ejecting | CrossDriver NTFS opens it read-only first, with one-click repair |
| Won't open as any format, or asks to be formatted | Damaged file system | Scan read-only with NAS Rescue, which tries progressively more lenient mount methods |
| Extremely slow, copy errors, keeps disconnecting | Bad sectors | Image it with NAS Rescue first, then find files in the image |
| BitLocker-encrypted drives | Needs the password or recovery key | Unlock and read it with CrossDriver NTFS or NAS Rescue |
| Clicking, not spinning, or not detected at all | Physical failure | Power it off now and take it to a professional data recovery service |
Wrong format or damaged? Take a read-only look 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.
- 1
Connect the drives
When you see "The disk you attached was not readable by this computer," click "Ignore."
- 2
Check health
In NAS Rescue, select the drive and turn on "Check disk health first (SMART + read test)." It takes about 30 seconds per disk. If it says "Image first," follow the steps for drives with bad sectors.
- 3
Scan and preview
Click "Scan Disks" and the volumes that can be opened are listed. Browse for free, and open photos, videos, and documents to check them.
- 4
Recovery
After upgrading to Pro, copy to another disk with each file verified by SHA-256; anything unreadable is logged in the report.
Q&A
The external drive's light is on, but my Mac won't read it. Is it broken?
Not necessarily. The light only means it has power. Check whether the drive appears in Disk Utility: if it does, it's most likely a format or file system problem and the data is still there; if it doesn't, try another cable, port, or enclosure.
My external hard drive won't read. Can the data be recovered?
In most cases, yes. As long as the Mac still detects the drive, you can scan it read-only and preview for free. If it isn't detected at all or makes strange noises, take it to a professional.
Can I just format it on the Mac?
Yes, but that erases the data on it. If the data matters, get your files out first, then format.
Neither my Mac nor a Windows PC can read it. What now?
If neither can read it, it's most likely a damaged file system, bad sectors, or a hardware problem, not a format compatibility issue. First confirm that the drive shows up in Disk Utility, then scan it read-only with NAS Rescue.
Can I recover files I deleted by mistake?
Not yet. NAS Rescue can't recover deleted files or files from a formatted drive; that needs a deep scan, which isn't supported yet.
Related products and guides
CrossDriver NAS Rescue
Drives that won't open, won't read, or have bad sectors: scan read-only and preview for free.
Recover data from a drive with bad sectors on Mac
Drive with bad sectors? Image it first, then find files in the image.
Mac external drive is read-only
What to do when an external drive is read-only on a Mac.
How to open Ext4, XFS, and other Linux drives on Mac
Open Ext4, XFS, Btrfs and other Linux drives on Mac.
See whether your files are still there
Download NAS Rescue: read-only scan, free preview.
Download for Mac — Free Scan & Preview