Hard drive has bad sectors?
Image it first, then find your files
Every extra read of a drive with bad sectors can damage more of it. The right order: copy everything still readable into a disk image, go back and slowly retry the bad areas, then read only from the image and let the original drive rest.
Good areas first, bad areas retried laterResumableBrowse while imagingRead-only throughoutLast updated
These signs usually mean bad sectors
Slower and slower
Folders take ages to open, and copy speed drops from tens of MB/s to a few KB/s.
Copies fail partway
Finder says an unexpected error occurred, and the same file fails at the same point every time.
Keeps disconnecting
The drive suddenly disappears when reading a certain spot, then comes back a moment later.
Clicking or not spinning
That's a head or motor failure, not bad sectors. Power it off now and take it to a professional data recovery service.
What a drive with bad sectors can't take
Don't run a "bad sector repair"
Scan-and-repair tools read the whole drive from start to finish and rewrite bad sectors, which is exactly what a failing drive can least handle.
Don't copy whole folders directly
When Finder hits a bad block, it retries over and over and hangs, wearing out the good areas too.
Don't format it
Formatting won't fix bad sectors; it only makes your files harder to find.
Get a large disk ready
The disk image is as large as the original drive, so the target disk needs more free space than the original's capacity.
Image a drive with bad sectors using 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. Imaging requires Pro; scanning, health checks, and previews are free.
- 1
Check health
Select the drive and turn on "Check disk health first (SMART + read test)." It reads SMART data and measures actual read speed, and shows "Image first" if it finds a problem. USB enclosures often don't pass SMART through; in that case, go by the read test.
- 2
Start imaging
In Tools › Imaging, choose a workspace on another disk and click "Start imaging." It quickly copies all the good areas first, then goes back to retry the bad ones. You can pause at any time and pick up where you left off.
- 3
Browse the image
Once part of the drive is imaged, you can click "Browse images": the volume opens from the image, and the original drive is no longer read. Areas not yet copied show as empty for now and fill in when you refresh.
- 4
Recover files
Copy the files to another disk. Unreadable blocks are skipped and logged in the report instead of stalling the whole job, and each file is verified with SHA-256.
Q&A
Can data be recovered from a hard drive with bad sectors?
In most cases, yes. Bad sectors usually make up only a small part of a drive. Image it first to copy the good areas in full, and nearly all your files can be recovered; the few files that sit in bad areas may be incomplete, and the report lists them.
How long does imaging take?
Good areas go at the drive's read speed, roughly 2–4 hours per 1 TB; the more bad areas, the slower it gets. You can copy the good areas and start finding files first, and let the bad-area retries run later.
What if the power goes out or the drive gets unplugged midway?
No problem. Imaging keeps track of which areas have been copied and which are bad, so when you start again, it picks up where it stopped.
Does this work for SSDs too?
You can image an SSD. But when an SSD fails, it often becomes unreadable all at once; software can't help with that, so take it to a professional.
Can bad sectors be repaired?
Physical bad sectors can't be repaired. Once your data is out, don't use that drive for important files again.
Related products and guides
CrossDriver NAS Rescue
Image drives with bad sectors first, then find files in the image—NAS drives included.
External hard drive not reading on Mac
External drive won't read on a Mac? Troubleshoot by symptom.
USB drive says it needs to be formatted
When a USB stick or external drive asks to be formatted, don't click yet.
Every read you save improves your chances
Download NAS Rescue and check drive health, scan, and preview for free first.
Download for Mac — Free Scan & Preview