What is a Hard Drive Bad Sector?
A bad sector is a cluster of storage space on a hard drive that has become inaccessible and unreadable (Wikipedia, 2022). Bad sectors form over time as a hard drive ages and its magnetic storage surface wears down. They can also occur suddenly due to physical shock, contamination, or overheating of the drive.
Signs of bad sectors include slower drive performance, file read/write errors, and inability of the drive to read data in certain areas. The consequences depend on the extent of bad sectors. A few bad sectors may just lower performance slightly, but a large number can cause crashes, data corruption, and total drive failure.
When the hard drive detects a bad sector, it marks it to prevent further writes to that area. The data is usually irrecoverable. The drive relies on redundancy and error correction to reconstruct lost data from good sectors when possible (How-To Geek, 2013). But extensive bad sectors will eventually lead to irreparable data loss and drive failure.
How Bad Sectors Affect Performance
Bad sectors can significantly impact hard drive performance in several ways:
Slow response times – As the hard drive attempts to read data from a bad sector, it will retry multiple times before giving up and reporting an error. This causes increased latency and slow response times.1
Long load times – Programs and files will take longer to load as they are located across bad sectors. The hard drive needs to work harder to retrieve all the associated data, despite errors.
Difficulty writing/reading data – With bad sectors unable to reliably store data, read/write operations become increasingly difficult for the hard drive controller.
Data corruption – If data is written to a bad sector, it can become lost or corrupted. The system may freeze attempting to read corrupt files.
Fixing Bad Sectors
There are several methods for attempting to fix bad sectors on a hard drive:
Built-in Disk Utilities
Windows includes the CHKDSK utility that can scan drives and detect bad sectors. Running CHKDSK with the “/R” parameter instructs it to locate and recover readable data from bad sectors, then remap those sectors as good (source). This may help fix some bad sectors, but is not a permanent solution.
Third Party Software
Specialized third party tools like HDD Regenerator can scan drives at a low level to identify and repair bad sectors. They use advanced algorithms to repair damaged disk surfaces and remapping techniques to put those sectors back into use (source).
Low Level Formatting
Manually re-formatting the hard drive at a low level can force the drive to remap bad sectors. However, this erases all data on the disk. Many modern hard drives do not support full low level formatting.
Re-mapping Bad Sectors
Hard drives themselves include spare sectors that can transparently remap bad sectors to good ones. However, once these spares are exhausted, the drive will be unable to remap additional bad sectors.
Data Recovery from Bad Sectors
One option for recovering data from a hard drive with bad sectors is to clone the drive before attempting data recovery. Cloning makes an exact copy of the drive, bad sectors and all, onto a new healthy drive (source). This protects the data from further damage during recovery efforts.
Once cloned, specialized data recovery software can help extract data from the bad sectors. Programs like Disk Drill, EaseUS Data Recovery Wizard (Freeware), and DiskGenius (Shareware) are designed to skip over bad sectors and recover data from the remaining readable portions of the drive (source).
For drives with extensive bad sector damage, a professional data recovery service may be required. They have specialized tools and clean room facilities to physically repair drives and extract data unreadable by software alone.
Preventing Bad Sectors
There are several steps you can take to try to prevent bad sectors from developing on your hard drive:
Handle drives carefully – Be gentle with your hard drive and avoid physical shocks or impacts which can damage the platters and lead to bad sectors. Don’t move your computer while the drive is spinning.
Proper shutdowns – Always use the proper shutdown procedure for your OS rather than just cutting power. Abruptly cutting power could damage data that is in the process of being written.
Defragment regularly – Defragmenting realigns data so it is contiguous on the drive, which reduces wear and tear that can lead to bad sectors forming over time. Defrag at least monthly.
Monitor SMART data – Use a tool like Auslogics Disk Defrag to monitor SMART attributes like reallocated sectors to catch issues early.
When to Replace a Drive
There are several signs that indicate it’s time to replace a hard drive that has bad sectors:
If the drive has accumulated a large number of bad sectors that cannot be repaired or remapped, this indicates the drive’s physical components are degrading. Most experts recommend replacing a hard drive once it develops more than 100 unfixable bad sectors (Source).
Frequent S.M.A.R.T. errors reported for attributes like reallocated sectors count, seek errors, or hardware ECC recovered indicate problems with the drive’s mechanics. If S.M.A.R.T. errors persist despite attempted fixes, the drive should be replaced.
If cloning software fails repeatedly when trying to clone or image the drive, even after reattempts, this suggests unrecoverable read/write issues. A failing drive that cannot be reliably cloned is unreliable for continued use.
Though a small number of bad sectors can be remapped, at a certain point the accumulation of physical bad sectors indicates component failure. Drives developing many bad sectors often continue degrading. When replacement is financially feasible, it is recommended for drives with substantial bad sectors.
Choosing a Replacement Drive
When it’s time to replace a hard drive due to bad sectors, you’ll want to choose a new drive that is compatible with your computer. Here are some key considerations:
Match interface and form factor – Make sure the new drive uses the same interface (SATA, IDE, etc.) and has the same physical size and shape as the old drive so it fits correctly in your computer.[1]
Get equal or larger capacity – Choose a new hard drive that has the same or higher storage capacity as your old drive. This ensures you don’t lose any storage space.[2]
Consider SSD instead of HDD – Solid state drives (SSDs) have faster performance, use less power, and are less prone to mechanical failure than traditional hard disk drives (HDDs). While SSDs are typically more expensive, prices have dropped significantly, so upgrading to an SSD may be worthwhile.[3]
Securely Wiping the Old Drive
It is extremely important to securely erase an old hard drive before disposing of it or selling it to protect sensitive data. Simply deleting files or formatting the drive does not actually remove the underlying data – it just removes the links to it. The data itself remains on the drive and could potentially be recovered. Secure erasure overwrites all sectors of the drive with random data to make previous data unrecoverable.
There are several software tools available to securely erase hard drives. Some popular free options include Darik’s Boot and Nuke (DBAN), Parted Magic, and Secure Eraser. These tools completely overwrite all data on the drive with random 1s and 0s. Multiple overwrite passes provide greater security. Other paid tools like CCleaner also offer secure erase functions.
For ultimate security, physical destruction or degaussing can be used in addition to secure erasure. Physically destroying the drive platters damages the magnetic surface so data cannot be read. Degaussing exposes the drive to a strong magnetic field that removes all magnetic data encoding. However, secure erasure software provides sufficient security for most home uses.
Migrating Data to the New Drive
There are a few options for migrating your data from the old hard drive to the new hard drive:
Using cloning software: Cloning software like Macrium Reflect or Clonezilla allows you to make an exact copy of your old hard drive and transfer it to the new drive. This replicates everything on the old drive including the operating system, programs, settings, and files. Cloning is fast and preserves the exact setup you had before.
Manual file copy/transfer: You can manually copy files and folders from the old drive to the new drive. This gives you more control over what gets transferred, but takes more time and effort. You’ll need to reinstall programs and the OS on the new drive.
Restoring from backups: If you have a full system backup image, you can restore it to the new drive to migrate your data. This is dependent on having a recent backup available.
Verifying Successful Data Migration
Once the data migration process is complete, it is crucial to verify that all files and data were successfully transferred from the old drive to the new drive. There are a few best practices for verifying a successful migration:
Compare file counts and sizes between the old and new drive to ensure no data was lost or corrupted during transfer. Tools like vSAN Data Migration provide pre-checks and post-checks to validate migration success.
Spot check random files on the new drive by opening them to verify they transferred correctly and are accessible. Pay extra attention to larger files like videos and collections of photos.
Test system functionality on the new drive by running applications, opening/saving files, etc. Confirm all programs, settings and data are present and working as expected post-migration.
Running thorough checks like these ensures all data made it to the new drive intact, with no corruption or loss, before wiping the old drive.