What happens if I scan and fix my external hard drive?

Having issues with your external hard drive like data corruption or slow performance? Running a scan and attempting to fix errors on an external hard drive is often a good first step before taking more drastic measures like formatting or replacing the drive. But what exactly happens when you try to scan and repair external hard drives? Let’s take a deeper look.

How Scanning Works

Scanning an external hard drive involves software searching through the drive and analyzing the contents. Different programs use different methods, but the goal is to identify any errors or problems that could be impacting performance or data integrity.

Typical things that a scan searches for include:

  • Bad sectors – Areas of the physical drive platter that can no longer reliably store data
  • File system errors – Problems with the data structure used to organize data on the drive
  • Lost clusters – Data fragments that are not linked properly on the drive
  • Cross-linked files – Parts of files that erroneously point to other files
  • Directory errors – Issues with the hierarchical file storage structure

To find these types of problems, the scanning software will analyze the disk sector by sector, reviewing the integrity of the formatting, data contents, and file system links. It may also directly test problem areas by writing sample data and reading it back to see if it matches.

Fixing Errors

Once a scan has identified issues, the repair aspect will attempt to fix them. The exact methods depend on the specific error and software being used, but some examples include:

  • Bad sectors – Marking the sectors as unusable so no data is stored there
  • File system errors – Rebuilding data structures like the partition table or directory tree
  • Cross-linked files – Separating files so they no longer erroneously share clusters
  • Directory issues – Recreating missing folders or reforming the folder tree

The process aims to rebuild any damaged or missing data structures while preserving the integrity of your actual files and data as much as possible. But some repairs may involve some data loss if the original contents cannot be recovered.

Tools for Scanning and Repairing

There are a variety of tools available for scanning and repairing external hard drives, depending on your operating system and needs.


  • CHKDSK – A built-in Windows command line tool for detecting and repairing file system issues.
  • SFC – System File Checker can scan and replace corrupted system files.
  • DiskChecker – Third party tool to scan, diagnose, and fix external drive errors.
  • HDD Regenerator – Repairs bad sectors and file system issues.


  • Disk Utility – Apple’s built-in disk repair program.
  • Drive Genius – Scans, optimizes, and repairs external drives.
  • TechTool Pro – Comprehensive diagnostics and repairs.
  • Alsoft DiskWarrior – Optimized for rebuilding directories and file structures.


  • fsck – File system check and repair tool.
  • GNOME Disks – GUI disk utility with diagnostics and fixes.
  • Disks – Another GUI disk utility for Linux systems.

Third party tools are available across platforms that may provide more advanced diagnostics and broader repair capabilities than built-in options.

Risks of Repairing an External Hard Drive

While the goal of scanning and repairing is to fix issues and recover data, there are some risks involved:

  • Repairs can take a long time to complete, ranging from hours to days depending on the drive size and number of errors.
  • Some repairs may be unable to fully recover all corrupted data.
  • Fixing some problems requires completely reformatting, which will erase all data.
  • Repair tools could potentially damage the file system further if improperly used.
  • Bad sectors often spread, potentially requiring replacement of the drive.

It’s a good idea to backup any important data on the external drive before attempting repairs in case anything goes wrong or data is altered or lost in the process.

Should I Repair Errors or Just Format the Drive?

If your external hard drive is showing signs of errors like malfunctioning, corruption, or slow performance, scanning and repairing it may identify and resolve the underlying issues. However, if the drive is severely damaged with lots of bad sectors or errors across multiple core components, fixing it may be unreliable or only provide temporary improvement before further issues arise again.

In situations where there are severe and widespread errors, it is often better to simply format or repartition the drive, erasing its contents but providing a fresh, clean slate. Formatting overwrites the existing file system and data structures, replacing any corrupted elements. This gives you the best chance of reliably using the external drive again, even if you lose the data on it.

So you need to weigh the value of the data on the external drive vs. the feasibility of actually repairing it. If the data is expendable or you have backups, formatting is usually the most effective solution for major systemic issues. But scanning and targeted repairs can be worthwhile if you need to recover irreplaceable data or there are only minor errors you hope to fix without a full erase.

Should I Scan and Repair Regularly?

While you can scan and repair an external hard drive at any time, doing it regularly as preventative maintenance is not usually necessary for most users. Unlike internal system drives, external drives typically see infrequent and intermittent use, reducing wear and the accumulation of errors over time. The exception is if you heavily rely on the same external drive for daily operations.

Some signs it may be wise to perform periodic checkups on an external drive include:

  • You use it to store only your most critical or hard to replace data.
  • It gets heavy daily or weekly use.
  • You frequently transport or travel with it.
  • It has previously shown errors or slow performance.

For such drives critical to your workflow, doing read-only diagnostic scans around once a month can identify problems early, and enable repairs before any serious corruption happens. But for more casual external storage that sees infrequent use, only scan when you actually suspect issues or notice behavior changes.

When to Consider Replacing an External Hard Drive

If your drive is showing frequent errors and performance issues even after multiple repair attempts, it may be time to replace it instead. Some signs a drive is too far gone include:

  • Bad sectors continue spreading after repairs
  • Recurring critical file system damage
  • Frequent crashes and failed operations
  • Extremely slow transfer speeds and performance

Continuing to use a severely damaged drive can result in further data loss. While repairs may seem to address problems temporarily, if problems return quickly it indicates fundamental physical failure is occurring. At that point, it’s safest to replace the external hard drive with a new one to avoid losing important data someday when the old one finally wears out for good.

Data Recovery Options Before Formatting or Replacing

If your external hard drive is damaged and you need to erase or replace it, don’t panic about losing all your data. There are still options you may be able to try recovering some or all of your important files first:

  • Try data recovery software that can read and extract data from corrupted drives.
  • Use specialized data recovery services that can repair drives in a sterile cleanroom environment.
  • If the circuitry in the USB enclosure has failed, remove the actual hard drive and connect it directly inside a desktop PC or another external enclosure.
  • In some cases it may be possible to transplant the drive platters into an identical functional drive to access the data.

These options can be expensive and time consuming, but may be worth it to recover critical files and precious memories before they are lost forever.

Example Scenario

Here is an example covering the key questions and decision points when dealing with errors on an external hard drive:

  • You rely on an external hard drive for storing photos and documents, but begin experiencing frequent crashes and slow performance when using it.
  • You scan the drive using Disk Utility on your Mac, and it reports file system corruption and bad sectors.
  • Can the errors be repaired? You run Disk Utility’s repair feature but it is unable to fix all the issues, so a full fix seems uncertain.
  • Is the data expendable? Many of the photos and documents are important records you want to preserve if possible.
  • You backup the recoverable data to a separate drive, then format the external drive to do a fresh install of the file system.
  • The problems disappear at first, but after a few weeks they start occurring again.
  • At this point it’s clear the drive has fundamental physical problems and continuing to use it carries a high risk of further data loss.
  • You replace it with a new external hard drive, and transfer the data you had backed up onto it.

While the damaged external drive couldn’t be permanently repaired or saved, you were able to recover the most important data before it completely failed by utilizing backups and recovery tools.


Scanning and repairing an external hard drive that is malfunctioning or corrupted can help resolve issues without losing data, as long as the damage is not too severe. But at a certain point, recurring or spreading errors indicate the drive is permanently failing and further repairs will be unreliable. At that stage, recovering data before it is lost becomes the top priority. With the right tools and techniques, you can often salvage important files even from damaged drives, preventing catastrophe through proactive action.

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