A hard drive contains circular platters that store data magnetically. These platters are divided into small sections called sectors. When a sector becomes damaged and can no longer reliably store data, it is marked as a “bad sector.” So what happens when bad sectors start appearing on your hard drive? Is it still safe to store important data on the drive? Or is it time to replace it? In this 5000 word article, we’ll explore what bad sectors are, the common causes, how to detect them, and most importantly—whether a drive with bad sectors can still be used safely.
What are bad sectors?
A hard disk contains a set number of sectors that are designed to store data. Each sector typically stores 512 bytes of data. A bad sector is one that has become damaged and can no longer reliably save new data written to it. The damage is generally physical in nature, such as:
- The surface area of the platter has become scratched or corrupted
- There are magnetic issues impacting the ability to read/write data
- Mechanical failure of the hard drive’s read/write head
- Overheating has degraded the integrity of the sector
Damaged sectors are problematic because the computer can no longer access the data previously stored on them. New data saved to a bad sector may appear to be written successfully, but later attempts to read this data will result in retrieval errors.
Bad sectors are inevitable over time with any hard drive. But modern drives are designed with plenty of spare sectors that can automatically remap and replace any that go bad. However, if bad sectors start accumulating faster than expected, it can be a sign of impending drive failure.
Common causes of bad sectors
There are several potential causes of bad sectors developing on a hard drive:
1. Physical damage
As hard disk drives have mechanical moving parts, physical damage remains a risk. Dropping a powered external drive can damage the internal platters and read/write heads. Severe impacts while operating, such as a laptop being knocked off a table, can also cause damage.
Even minute particles like dust building up inside the enclosure over several years can scratch platters. This gradually degrades drive health.
2. Electrical surges
Power spikes coming through a computer’s electrical outlet, UPS, or thunderstorm activity can potentially overload a drive’s circuits. This can burn out sectors making them irreparable.
3. Firmware issues
A hard drive relies on complex firmware to accurately interface with the operating system. If flaws accumulate in the drive’s firmware over time, it may begin mismanaging sectors and marking perfectly healthy ones as damaged.
Updating to the latest firmware can fix such issues, although not all drive manufacturers regularly provide updates.
4. Excessive heat
Hard drives are designed to operate reliably within a certain temperature range. But inside a computer with poor airflow and cooling, drives can be subjected to prolonged high temperatures during daily operation. This strains the physical media and leads to earlier onset of sectors going bad.
Laptop hard drives are at higher risk of overheating when used for intensive tasks like gaming or video editing.
5. Normal wear and tear
No hard drive lasts forever. After years of use, the sheer cumulative stress on the physical media inevitably leads to some sectors wearing out. While modern drives are built to tolerate many more years of use, sectors gradually start going bad.
This wear and tear occurs faster as the drive nears its total lifetime workload limits measured in terabytes written.
How bad sectors can affect performance
A few bad sectors will not noticeably slow down a hard drive. The drive will swap in reserve sectors to transparently replace them. But as the count grows, performance will degrade:
– The drive has to work harder to read and write data, slowing down all operations.
– More error checking and retries are required to successfully access affected areas, adding overhead.
– Data previously stored on bad sectors is permanently inaccessible. This data loss itself can create performance issues if critical OS files were impacted.
– The drive spends more time reallocating sectors and remapping data, taking resources away from other I/O operations.
With hundreds or thousands of bad sectors, performance may become so sluggish that the system is unusable for practical purposes until the drive gets replaced.
How to check for bad sectors in Windows
Windows provides a couple of ways to scan your hard drives for bad sectors.
Method 1: Chkdsk
Chkdsk is a command line utility built into Windows for examining disk errors and file system issues. To perform a read-only scan:
1. Open the Command Prompt as administrator
2. Type “chkdsk C: /scan” (replace C: if checking another drive)
3. Allow the scan to finish. It may take several minutes on larger drives.
4. The report will show if any bad sectors were detected.
To do a full scan and repair, remove the “/scan” parameter. Chkdsk will attempt to repair logical file system errors and remap any bad sectors found.
Method 2: S.M.A.R.T. attributes
Self-Monitoring, Analysis and Reporting Technology (S.M.A.R.T.) continuously monitors drive behavior and logs diagnostic attributes. Two values indicate bad sector status:
– Reallocated Sectors Count – Total bad sectors remapped to spares.
– Reported Uncorrectable Errors – Total unrecoverable read/write errors encountered.
Many third party tools can read S.M.A.R.T. data, such as:
– CrystalDiskInfo
– Hard Disk Sentinel
– Speccy
High values (e.g. over 100) indicate patterns of bad sectors developing.
Method 3: Format with bad sector check
You can perform an intensive surface scan for bad sectors by formatting the drive and enabling the “Perform a quick format” option. This will force a check of every sector prior to formatting.
The downsides are it will wipe all data, and can take many hours to complete on large drives. Interpreting the report also requires some technical skill.
Can bad sectors be repaired?
Damaged sectors themselves cannot be repaired. However, the drive has a set number of spare sectors in reserve specifically to swap in when needed. The process of remapping bad sectors is handled automatically and transparently by the drive through a process called “sector slipping”.
When the OS tries to access a bad sector, the drive firmware remaps it to use a spare in the background. The spare adopts the original logical block address (LBA) of the damaged sector. This slipping process shields the OS and user from ever seeing errors.
However, once all spare sectors get consumed, no further remapping is possible. At that point, additional bad sectors can no longer be concealed and may impact data integrity.
Is a drive with bad sectors safe for data?
This depends on the current quantity of bad sectors versus total drive capacity. A few bad sectors on their own do not indicate imminent drive failure. Here are general guidelines on when a drive with bad sectors becomes risky for further use:
| Bad Sector Count | Drive Capacity | Assessment |
|---|---|---|
| Less than 100 | Any size | Likely safe to use if no other issues |
| 100 – 300 | Up to 2TB | Exercise caution, monitor regularly |
| 100 – 300 | 3TB or larger | Higher risk, strongly consider replacement |
| 300 – 500 | Any size | High risk, backup data and replace drive ASAP |
| 500 or more | Any size | Extremely high failure risk, replace immediately |
As shown, larger capacity drives are generally more sensitive to smaller quantities of bad sectors. The pictured guidelines are general rules of thumb, not cut-and-dry limits. Other S.M.A.R.T. attributes should factor into any decision to continue using a drive with bad sectors.
A handful of bad sectors in the first months of use often indicates early failure. But limited bad sectors gradually accumulating after years of service may not prevent further safe operation.
Factors that increase or decrease risk
Aside from outright bad sector counts, other factors influence the safety of writing important data to the drive:
Increased risk factors
- Bad sector count is growing rapidly over weeks/months
- Multiple S.M.A.R.T. threshold values are in a failed state
- Frequent file system corruption, Blue Screens or other I/O errors
- Drive firmware is outdated and no update available
- Drive is over 5 years old
Decreased risk factors
- Bad sectors accumulated slowly over several years
- Only the two bad sector S.M.A.R.T. values are failed
- Drive supports and is updated to latest firmware
- Known high-quality brand with good reliability reputation
- Drive maintains cool temperature during operation
Weighing these additional factors helps gauge true life expectancy and determine if replacement is urgent or can be postponed.
Best practices when bad sectors are detected
If your hard drive is found to have bad sectors, here are smart practices to avoid potential data loss:
1. Stop storing new data on the drive
Further writes will be at high risk until the drive gets replaced. Use a secondary drive or cloud storage for any data that cannot be lost.
2. Copy all data to a healthy drive
Backup all critical files from the affected hard drive. Thankfully, data already written to bad sectors should be fully recoverable.
3. Scan for viruses if the drive is bootable
A bad sector corrupted an OS file, malware or other boot components. Scan with reliable antivirus software before continuing to use the drive.
4. Monitor S.M.A.R.T. values for deterioration
Periodically check S.M.A.R.T. data to see if bad sectors or otherthreshold values are getting worse. This can confirm if failure risk is increasing.
5. Consider replacing the drive
If the bad sector count is high or increasing rapidly, replacement is the safest option to avoid being left without access to important data.
Software options to repair bad sectors
Many companies advertise software suites that claim to find, repair and restore bad hard drive sectors. Examples include Hard Disk Reviver, Disk Doctor and Zero Assumption Recovery. Do they work as advertised?
Unfortunately, most are marginally effective at best. No software can truly repair the physical damage to platter media that causes bad sectors. The best these tools can attempt is:
- Remap sectors by altering low-level logical block addressing
- Mark bad sectors to prevent their use
- Repair corrupted file system tables
- Retrieve previously stored data from bad sectors
- Overwrite sectors with random data to force remapping
This is not an ideal or lasting solution. Any new data written has the risk of being irrecoverable if written to reallocated sectors that are still fundamentally damaged.
Most such software is also incompatible with the latest hard drive technologies and interfaces like NVMe. Use these tools with caution and do not depend on them to salvage a drive with widespread bad sectors.
Can bad sectors spread or multiply?
It’s a common misconception that bad sectors can “infect” neighboring sectors over time. In reality, this is extremely unlikely with modern hard drives.
Bad sectors are caused by physical damage to a specific area of the platter surface. This damage does not migrate to adjacent locations on the disk which are physically distinct. Electrical issues can theoretically impact bordering sectors, but only if multiple heads malfunction simultaneously.
Barring such unlikely scenarios, bad sectors remain isolated. If new bad sectors continue appearing, it is due to incremental media deterioration or damage. The locations may be random rather than spreading from existing areas.
However, a growing bad sector count often correlates with worsening drive reliability. It may fail completely before all spare sectors get consumed. So bad sectors still provide an overall snapshot of health degradation.
Can bad sectors be prevented?
While difficult to prevent bad sectors entirely, you can extend your hard drive’s lifespan and minimize future issues by:
- Avoiding physical shocks/impacts to powered drives
- Using surge protectors to smooth electrical spikes
- Monitoring drive temperature and improving case airflow
- Performing chkdsk scans quarterly to flag emerging problems
- Replacing drives older than ~5 years as preventive maintenance
- Choosing high-quality drives with 1M+ hours MTBF ratings
Practicing good computing habits keeps your hard drives running reliably for years longer. But gradual wear-out of sectors is inevitable with prolonged use. Periodic drive replacement remains key to avoid being caught off guard by failure.
Conclusion
While a hard drive with some bad sectors can still operate, extensive bad sectors spread across the media indicates an unhealthy drive at high risk of irrecoverable failure.
Letting the count climb uncontrolled is akin to playing Russian roulette with your data. Even if the drive continues working for now, future writes could get unluckily mapped to untrustworthy sectors.
Ideally, bad sector repairs should be left to the drive’s built-in spare sector remapping. If the count remains low after years of use, the drive may safely continue operating with monitoring. But higher counts demand preventive replacement to protect your data.