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[ The PC Guide | System Care Guide | Data Loss and Virus Prevention | Data Problem Detection ]

Detecting Hard Disk Read Errors

There are many different ways that hard disks can fail. This can be very distressing, because unlike virtually every other part of your PC, when your hard disk dies, it takes your data with it. If your keyboard or modem or monitor stops working, it can be expensive to fix the problem but your files will still be where you left them. Hard disk reliability issues are discussed in detail here.

Many hard drives fail with a bang: one day the drive, instead of spinning up and booting the PC, may go "klunk, klunk, klunk" and then spin down again, and that may be the last you ever see of whatever is on it (unless you have backups). However, many drives fail with a whimper; they slowly develop problems, and if you are astute in detecting them, you can sometimes avoid a catastrophe.

One of the ways that early problems with hard disks manifest themselves is with problems reading a particular area of the disk: a read error. If the disk develops a bad spot where it can no longer reliably read what is written there, you will not know this until you try to read from the sector where the problem is. If it is occupied by a seldom-used file, you may not notice for weeks or months. However, many drives start out with a handful of bad sectors and then develop more later on. This doesn't always happen, but it does often enough that it is very useful to detect these read errors as quickly as possible.

For this reason, utility programs were developed that test the surface of a disk for read errors. They scan over the surface of the disk and read the contents of every sector, looking for problems, and report if any are found. This increases the chances of detecting a problem with your hard disk when it occurs first with seldom-accessed files, before it spreads to more important parts of the disk.

The most common disk error checkers are in fact part of the same utilities that scan for file system corruption--Microsoft's Scandisk and Norton's Disk Doctor. Even though the same utility scans for both file system problems and read errors, recognize that these are very different problems that are being detected. These programs often call the portion of their work where disk read errors are detected the "Surface Scan" or "Surface Test", referring to the platter surfaces on the disk where the data is stored.

In virtually every case, it takes a lot longer to scan an entire disk volume for errors than it does to check out its file system structures. It also is far less common to actually find a problem. For this reason, I recommend that scans of the disk surface for read errors be done only weekly (not daily like the file system checks.) If you suspect problems with your disk, you may want to increase the frequency with which you run the utility. Since disk scanning can take a fair bit of time, I usually recommend that people use a program scheduler to automate the task, running it when they are not using their PC.

Warning: Always use the proper tool for your operating system. Do not use old versions of SCANDISK etc. on newer systems running Windows 95, for example. And make sure that if you are using FAT32, that you use tools that are modern enough to recognize the newer file system.

Next: Virus Detection and Protection

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