In Mac OS X operating system, sometimes the same disk space might be allocated to two different files. This is called extent allocation problem. Though, it is quite rare situations, but still it happens. In such cases, any one of the affected Mac files has to be deleted. If fsck or Disk Utility tool reports the problem on Mac hard drive, you should not install any third-party application. This behavior removes your significant data file and cause critical data loss situations. In order to recover lost data in such cases, Mac recovery becomes need of hour.

How to fix Extent Allocation problem in Mac OS X using Disk Utility or fsck?

You can try solving the problem using Disk Utility in Mac OS X 10.4.2 or later. It can help you to overcome such problems without erasing entire volume. If your system or boot volume is not working properly, boot your system from Mac OS X 10.4.2 or later boot disk, and then run Disk Utility tool for repairing affected Mac volume...