I recently installed Norton Utilities and, during a surface scan of my hard disk, I noticed a number of bad clusters. The scan continued past them, didn't report any errors and these clusters are not yet interfering with used disk space. What is a bad cluster? What may have caused it? Can they spread or move? Will they affect the data on the disk and can I get rid of them?
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A bad cluster is a small block of disk space (usually 2KB or 4KB) that tests have determined cannot be written to and read from reliably. All disks have them, as it's not possible to make the magnetic recording surface absolutely perfect, although some drives hide from the user those that are found during manufacture.
New bad clusters can develop due to wear or a fault developing in the drive. They can also be caused by the magnetic surface being damaged - for example, if the system is bumped while the disk is being accessed.
Bad clusters cannot move. If they increase in number every time you do a surface scan this indicates that the drive is developing a fault and should be replaced. But if the number remains constant they are nothing to worry about. The clusters will not be used to store data, so there is absolutely no risk of data errors or data loss occurring because of them. See also tip What is a lost cluster?
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Introduction | General