What are bad sectors?
Bad sectors are areas on a hard disk drive that can no longer reliably store data due to physical damage or corruption. When a sector becomes bad, the operating system marks it as such and stops using it for file storage. Bad sectors most commonly develop due to physical damage to the disk surface, such as scratches or impacts while the drive is running. They can also occur due to gradual degradation of the disk media over time. Some key characteristics of bad sectors include:
- They are inaccessible and return errors when read from or written to
- They are identified and marked by the operating system so it won’t store files on them
- They can cause data loss or corruption if files are partially stored on them
- They gradually increase in number as the hard disk ages and deteriorates
Bad sectors indicate potential hard disk problems and imminent failure. As more develop over time, the disk will lose usable space and its performance will degrade. The only way to fix bad sectors is to replace the failing hard disk with a new one. But there are some techniques that can potentially repair individual bad sectors and prolong the lifespan of the drive.
Causes of Bad Sectors
There are several potential causes of bad sectors developing on a hard drive:
Physical Damage
The surface of a hard disk contains microscopic magnetic grains that store the data. If the disk surface is damaged due to scratches, impacts, wear and tear or contamination from particles, it can cause data loss in those areas resulting in bad sectors. Physical damage is one of the most common causes of bad sectors.
Manufacturing Defects
During the manufacturing process, defects might occur on the platters surface leading to regions prone to errors. These can develop into bad sectors with usage over time. Manufacturing quality control aims to minimize these, but some may still slip through.
Failed Writes
If a write operation to the disk is interrupted due to a power failure or system crash, it may result in an incomplete write. This can corrupt the sector and render it unusable. The operating system then flags the failed write sector as bad.
Degradation Over Time
As part of normal wear and tear, hard disks can deteriorate over years of intensive use. The magnetic media slowly degrades, making data storage less reliable and leading to bad sectors. This effect is accelerated by extreme storage conditions like high temperatures.
Firmware Bugs
Bugs in a hard disk’s firmware can very rarely cause bad sectors to start appearing. A firmware update may be required in such cases to fix the issue.
Signs of Bad Sectors
Here are some common signs of bad sectors on a hard drive:
- Files failing to copy or move to certain sectors
- Difficulty writing data to the disk, but reading existing data is fine
- The operating system prompting you to run CHKDSK scan due to file system errors
- Strange noises from the hard disk like clicks, buzzing or grinding
- Failure of sectors during the bad sector scan using HDD tools
- Data corruption like documents or photos opening with errors
- Blue screen crashes or operating system freezes
- Slower disk performance over time
If you suspect bad sectors, run a full disk scan using HDD tools to assess the physical health of the drive and confirm the bad areas. The sooner bad sectors are detected, the less likely extensive data loss will occur.
Can Bad Sectors be Repaired?
Strictly speaking, it’s not possible to repair bad sectors themselves. The physical surface damage or magnetic corruption remains even if sectors are remapped. However, the drive can be configured to remap the bad sectors so they are no longer used for storage. Remapping tricks the OS into avoiding the damaged areas entirely essentially masking the bad sectors.
Here are a few ways bad sectors can be remapped:
Drive Self-Monitoring and Remapping
Modern hard disks use advanced self-monitoring capabilities to detect errors during reads and writes. When sectors start failing, the drive firmware automatically remaps them by swapping them with spare sectors reserved for this purpose. However, the number of spare sectors is limited. Once exhausted, self-remapping is no longer possible.
Manual Remapping Using HDD Utilities
There are HDD utilities that can manually scan disks to identify bad sectors. Once found, they can force the hard disk to remap the failing sectors preventing their use. This reallocates the sectors without data loss. Tools such as HD Tune, Victoria and SeaTools have such remapping capabilities.
Low-Level Formatting
Formatting a drive erases it and recreates the file system. Full / low-level formatting can force reallocation of all sectors on the disk, including bad ones. However, this is destructive – all data is erased. It also reduces the drive’s lifespan if done frequently.
Sector Repair Using Firmware Commands
The ATA standard provides special firmware commands to force hard disks to internally reassign sectors. Utilities like HDDScan for Windows, GSmartControl for Linux and smartmontools can directly send these commands to the drive to replace bad sectors. However, this method does not work on all brands.
So in summary – bad sectors can’t be repaired, but disc utilities and firmware commands can remap them so they are no longer used for data storage. This extends the usable life of the aging drive.
Pros and Cons of Bad Sector Remapping
Remapping bad sectors has certain advantages and disadvantages:
Pros:
- Prevents loss of data stored on bad sectors
- Disk remains logically functional despite developing physical defects
- Errors and performance issues are minimized
- Adds days or weeks of usable life to failing or aged drives
- Avoids immediate data migration need if sectors can be remapped
Cons:
- Does not fix the underlying physical damage on the disk
- Gradual loss of spare sectors as more get remapped over time
- Performance degradation as sectors get swapped and remapped
- No guarantee bad sectors won’t reappear or get worse
- Doesn’t eliminate need to replace failing drive eventually
So remapping offers short-term benefits, but the disk health will continue to degrade. It should be seen as a stop-gap, not a permanent fix for bad sectors. Prolonged intensive use will cause physical defects to spread once spare sectors are exhausted.
Best Practices for Bad Sector Remapping
If you decide to remap bad sectors, follow these best practices:
- Backup data fully before attempting sector repairs
- Use reputed tools like HD Tune Pro or SeaTools – avoid untrusted software
- Scan for bad sectors first to identify extent of damage
- Research if manual remapping is recommended for your hard disk model
- Check logs after to confirm bad sector counts were reduced
- Monitor SMART parameters for signs of imminent failure
- Consider replacing the disk if too many sectors need remapping
While remapping can fix select bad sectors, it is not a permanent solution if physical degradation continues across the platters. The need for a new drive becomes unavoidable once original defects spread too far.
Steps to Remap Bad Sectors
Here is a general sequence of steps for remapping bad sectors on a hard disk:
- Back up your files and data fully as a precaution.
- Download and install a HDD utility like HD Tune Pro that supports manual remapping.
- Run a full scan for bad sectors using the tool.
- Note down the list and locations of any bad sectors detected.
- Use the tool’s commands to remap each bad sector to a reserved spare sector.
- Confirm the bad sector count reduced in a new scan after remapping.
- Monitor SMART stats and run occasional scans to check for new bad sectors.
- Consider replacing the aging disk if too many sectors need remapping.
The process varies slightly across tools, so refer to its documentation for the exact steps. Also research if manual remapping is recommended for your specific hard disk make and model before attempting it.
Physical Repair of Disk Platters
While software remapping tricks the OS into avoiding bad areas, the physical damage remains on the drive platters themselves. Research labs have explored more invasive physical techniques to repair the magnetic disk surface itself:
Magnetic Force Microscopy (MFM)
MFM uses a specialized microscope tip magnetized with an electric current to physically alter magnetic polarities on the platter surface and repair corruption. But it’s extremely complex and suited only for research.
Laser Assisted Magnetic Recording (LAMR)
LAMR focuses a laser on the disk platter to locally heat it. This allows the magnetic polarity of individual grains to be flipped using an external magnetic field. While promising, LAMR is not commercially viable currently.
Degaussing
Exposing damaged disk platters to strong alternating magnetic fields can realign the magnetic grains and restore corrupted polarity. However, this wipes data and risks further damage if not done properly.
So physical repair remains impractical. Software workarounds like remapping are the only feasible option currently for typical hard disk defects. Avoid DIY physical repair attempts as they usually destroy the drive and data.
When to Replace a Drive with Bad Sectors
While remapping buys some extra lifespan, it’s not wise to prolong the use of a severely degraded drive indefinitely. It’s advisable to replace a drive exhibiting the following despite remapping attempts:
- Thousands of bad sectors keep appearing across multiple platters
- SMART statistics show high and growing reallocated or pending sector counts
- Frequent Blue Screens of Death or operating system hangs
- Responding slowly despite troubleshooting steps
- Making abnormal noises during operation
- Experiencing overheating issues
The above are signs of unrecoverable failure looming. Allowing such a damaged drive to stay in service risks severe data loss when it ultimately stops working. Replacing it with a new hard disk is the prudent choice.
Data Recovery from Drives with Bad Sectors
Before disposal, you may want to attempt data recovery from old drives plagued by bad sectors:
Software Based Recovery
Specialized tools like ReclaiMe File Recovery ignore bad sectors and recover data based on file signatures. But software relies on sectors being readable, so may not work if damage is extensive.
Professional Recovery Service
For drives with thousands of bad sectors, professional data recovery may be the only option. Experts use specialized tools in dust-free clean rooms to extract data from degraded platters. But it’s expensive – upwards of $500 or more based on drive size.
Drive Transplant
This involves physically removing the platters from inside the damaged drive and implanting them in a donor drive for long enough to copy the data off. Needs technical skill and cleanroom. Destructive for original drive.
So before discarding old drives, explore data recovery options if they contained important files that weren’t backed up adequately elsewhere.
Preventing Bad Sectors
You can minimize the chances of bad sectors developing in the first place by:
- Using UPS systems to prevent sudden power loss during writes
- Making sure the drive does not overheat
- Avoiding shocks, drops, bumps to PC/laptop when powered on
- Using modern hard disks with embedded defect management
- Checking new HDDs for initial defects and returning if found
- Following storage guidelines of hard disk manufacturers
While total prevention is impossible over years of use, sensible usage and care reduces the risks of physical damage leading to bad sector formation.
Conclusion
Bad sectors are unavoidable as hard disks age and deteriorate. While they cannot be permanently fixed, disk utilities can remap bad areas so they are no longer used for data storage. This extends the usable lifespan of the drive. However, physical degradation will progress without platter repairs. So remapping is a temporary stopgap only, and drive replacement becomes necessary once defects spread too far. Handle drives developing multiple bad sectors cautiously and consider data recovery options before disposal. With proper care, prevention and monitoring, you can maximize a hard disk’s useful life span and minimize loss of files due to bad sectors.
