How to Repair Bad Sectors on an External Hard Drive on Mac Without Losing Data

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Bad sectors sound scary, right? After you learn what they are and what they can do, it's clear that you want them to be as few as possible. So if you're trying to fix bad sectors on an external hard drive on Mac without losing important data, the information here will be of great help.

What are bad sectors?

Wikipedia - "A bad sector is a permanently damaged area on a hard disk or other magnetic storage device. Once a sector is bad, all information stored in it is lost. After a bad sector is detected and marked, the operating system will skip over it in future reads and writes."

Logically, from the definition, we can infer that when a hard drive develops bad sectors, it is at risk of impending failure and permanent data loss.

Should you be alarmed when bad sectors are found? Since the operating system can still function normally by skipping over them, there is no need to panic when a few bad sectors are detected. However, if they continue to increase and affect system performance, action must be taken to repair them. Bad sectors on a hard drive are inevitable, so it is important to know how to minimize their occurrence and maintain the health of your hard drive in daily use.

There are two types of bad sectors that you should know about…

• Bad sectors from physical damage (hard bad sectors): Bad sectors caused by physical damage cannot be repaired. For example, scratches on the surface of the hard drive; critical components inside the sealed area are severely damaged by dust; rotating parts are damaged due to a hard drive crash. • Bad sectors from logical damage (soft bad sectors): Most bad sectors caused by logical errors can be fixed. What are these situations? Typically, sudden power outages while data is being written to the disk; virus or malware attacks, and so on.

How to Find Bad Sectors on a Mac?

First, you diagnose the disease.

While this is a risk, bad sectors typically don't need to be checked unless the hard drive is having trouble reading or writing to certain sectors, or the operating system is freezing up regularly.

Second, use professional software to run an automated check.

Otherwise, you can use third-party software to check your hard drive's health, including for bad sectors on a Mac. We find #Setapp# the most reliable.

How to Recover Data from a Bad Sector on a Mac

When bad sectors accumulate to a certain extent, the direct consequence is that they affect disk data. At this point, it's necessary to recover data from bad sectors, especially those without real-time backups. Usually, data in external storage devices with too many bad sectors cannot be accessed normally, and thus cannot be opened in a regular way. Fortunately, with the help of tools like Data Recovery Wizard for Mac, you can easily recover data from inaccessible hard drives, USB drives, or memory cards.

Download Mac hard drive recovery software, and follow the 3-step guide to retrieve data from bad sectors of an external hard drive.

Step 1: Select the location to scan

Launch the All-in-One Data Recovery Wizard for Mac, select the hard drive, SSD, SD card, USB flash drive, or TF card where you lost your data. Click “Search for Lost Files” to start scanning.

Note: Before you proceed with data recovery, it's recommended that you click “Disk Backup” from the left sidebar and create a backup of your Mac to prevent further data loss. After the backup, the software can recover data from the Mac backup, and your computer can write new data again.

Select a location and click "Search Lost Files".

Step 2. Filter Lost Mac Data

The software will automatically scan the lost data on your MacBook/iMac. After the scan, you can filter the required data by clicking the "Type" and "Path" buttons.

Step 3: Recover Lost Data or Files

Preview the files by double-clicking them. Then, click “Recover” to restore the lost data to another location.

A large number of bad sectors can prevent a Mac from booting. If your Mac fails to start up due to an unbootable hard drive, how can you recover data from the unbootable hard drive on Mac? Don't panic! You can resolve this issue without accessing the operating system by using Data Recovery Wizard for Mac Bootable Edition.

Please refer to the relevant page to learn how to create the Data Recovery Wizard for Mac bootable media.

How to Repair Bad Sectors on an External Hard Drive on a Mac (2 Methods)

As mentioned, hard bad sectors are effectively unfixable, but most soft bad sectors are recoverable. In fact, this isn't really a “repair” so much as it is reallocation: the disk tool will stop using the space on the drive that the bad sector occupies.

Fix 1: Repair Bad Sectors with Disk Utility's "First Aid"

• Connect the external hard drive to your Mac using the correct cable or enclosure.
• Press and hold Command + R until you see the Apple logo.
• In the macOS Utilities window, select Disk Utility, then click Continue.
• In Disk Utility's sidebar, select the connected external hard drive and click "First Aid."
• Click Run to repair the hard drive.

Solution 2: Replace the failed external drive using Disk Utility's Restore feature

Before your external hard drive fails completely, you can try cloning the hard drive and all its contents to a new one to prevent data loss.

• The target HDD should be the same size or larger than the original external hard drive. Connect both HDDs to your Mac before proceeding.
• Navigate to Applications > Utilities > Disk Utility.
• First, select the new hard drive from the sidebar, then click on Restore.
• Proceed by selecting "From" and then choose the failed external hard drive. Click Restore.
• Wait for Disk Utility to complete the cloning process. Once finished, click on Done.

What comes next, then...?

Bad sectors are unpredictable – you never know when and how they will occur. The only thing you can do is invest in some good security software or use an UPS device to prevent sudden power outages. While Data Recovery Wizard for Mac may help you recover data from bad sectors on an external hard drive, a more reliable method would be to regularly back up important files from your Mac's hard drive.