How to Repair Bad Sectors on a Hard Drive

Do you frequently get messages like 'Cyclic Redundancy Error', while retrieving data from your hard drive? Then you may be facing a bad sector problem. It frequently occurs in old and overused drives.

A computer hard drive is a magnetic storage disk, on which data is stored by changing of its magnetization states. The disk is designed to function as a data bank, with addresses for each region. It is divided into concentric tracks, starting from the center, towards the outer rim. These tracks are further divided into sectors, by radial division.

Every sector is a unit storage space, which holds about 512 bytes of data. On a hard drive, with a total memory capacity of 200 GB, there are as many as 400 million such sectors.

A bad sector is a physically damaged sector, which can no longer be accessed by the operating system. When it happens to be a region where you have stored data, you get 'cyclic redundancy error', as the operating system cannot retrieve data from that region.

To check for integrity of written data, parity checking bits are written, while storing it. The data may not be read, due to inconsistencies of parity checking bits, that are verified, while writing and reading.

The prime cause is a loss of magnetism on the hard drive surface, with time. They may also be caused by sudden physical shocks to the hard drive, sudden power shutdown, and interruption of reading and writing operations on the disk. A failing read-write head of a hard disk is another reason.

If the bad sectors are caused due to loss of magnetization, the damage is irreversible. However, if the problem is due to inconsistencies in parity checking bits, it can be corrected by using appropriate software, that can rewrite and restore these bits.

Taking into consideration that bad sectors will be eventually created over the usage life of the hard drive, manufacturers make a provision of unused spare sectors on the drive, which can be utilized. When the disk controller encounters a bad sector, it remaps data to a different spare sector, automatically.

If you are using a Windows operating system, there are two built-in programs, that you can use, to repair the sectors. One is the CHKDSK and a more advanced version of it called 'ScanDisk'.

To locate bad sectors and remap data to other spare sectors, the CHKDSK or ScanDisk utility writes on and reads every region of a drive volume. Once such a sector is detected, it is ensured that data is no longer written in that region and stored data is remapped to spare sectors.

Here is how you can fix the problem, by running the disk scan program on Windows Vista, Windows 7, Windows 8/10:

• Open 'My Computer' and right click on the drive volume, which is suspected to have bad sectors.

• Click on the 'Properties' option and select the 'Tools' tab, in the window that opens.

• Click on 'Check Now', under the 'Error Checking' section.

• Another window will open, with two check boxes that say, 'Automatically fix file system errors' and 'Scan for and attempt recovery of bad sectors'.

• Select both the options and click on 'Start'. Before clicking on 'Start', close all other programs, that are running on the OS. Else, the scanning program can only run when you restart your computer next time.

Using a power backup, like a UPS device and running regular disk fragmentation, might help in prolonging the life of your hard drive and prevent bad sectors from occurring.

Never shut down your computer by directly switching off the power button. Always switch it off, by selecting the shutdown option. This may prevent the bad sectors, that are created due to an improper shutdown.