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.
You can repair only Mac OS X Extended (Journaled) or Mac OS X Extended volumes (also called HFS Plus, HFS Plus volumes, or HFS Plus Journaled).
If you are using the Disk Utility tool on Mac OS X 10.4.2 or later boot DVD or fsck for repairing affected volume, you can review some of the affected files with the help of 'DamagedFiles' directory.
Check for Files:
When you use fsck or Disk Utility in Mac OS X 10.4.2 or later versions to fix the overlapped extent allocation problems, the below processes take place:
Repair utility tries to move data of overlapped file to new location.
If move completes successfully, file is updated for using new location.
If move fails, the data is not moved.
In case you don't have Mac OS X install disk or volume that you can use to boot your system, you should not install updates. It may cause further damage and cause severe data loss, putting you in need of mac disk recovery .
Recovery is best possible using advanced and powerful Mac recovery software. The applications do not modify original data on the hard drive as of their read-only and non-destructive conduct. The Mac recovery applications are incorporated with rich graphical user interface to offer easy recovery.
Stellar Phoenix Macintosh Data Recovery software salvages lost, deleted, missing, inaccessible, and unusable files from Mac hard drive. It works well with Mac OS X 10.6 Snow Leopard, 10.5 Leopard, 10.4 Tiger, and 10.3.9 Panther. The software retrieves data from HFS, HFS+, HFSX, HFS Wrapper, and FAT file system volumes.
Extent Allocation Issues and Data Loss in Mac OS X