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 the problem of having bad sectors on your hard drive. It is a frequent problem caused in old and overused hard drives.

What are Bad Sectors on Hard Drives?

Before we talk about how to fix bad sectors on hard drive, let us understand what we mean by bad sectors. 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 data 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 on hard drive is a physically damaged sector which can no longer be accessed by the operating system. When this bad sector happens to be a region where you have stored data, you get the '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 data on a hard drive. The data may not be read due to inconsistencies of parity checking bits that are verified while writing and reading data from a hard drive.

What Causes Bad Sectors on Hard Drives?

There are many reasons that can lead to a hard drive bad sector. The main reason for bad sectors is a loss of magnetism of the hard drive surface in certain areas with time. Bad sectors 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 cause of bad sectors getting created.

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.

How to Repair Bad Sectors

Let us now see how to go about repairing bad sectors on hard drive. 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 hard drive which can be utilized when bad sectors occur on a hard disk. When the disk controller encounters a bad sector, it remaps data to a different spare sector on a hard drive automatically. If you are using a windows operating system, there are two built-in programs that you can use to repair bad 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 hard drive volume. Once a bad 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 bad sectors by running the disk scan program on any Windows Operating system like Windows XP, Windows Vista and Windows 7:

• 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 operating system. Otherwise the scanning program can only run when you restart your computer next time.

Using a power back up 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 the power switch off. Always switch it off by selecting the shut down option. This may prevent the bad sectors that are created due to improper shut down.