´Missing Extent´ Error in Mac

On Mac OS X hard disk, a file usually exits as fragments. Mac systems refer these fragments as extents. To hold information about these fragments, a catalog file, called as extents B-tree, is used. But sometimes, you may observe errors with these extents. In such cases, the corresponding file becomes inaccessible to the system. Disk Utility and fsck can detect such files. However to recover the lost file, you require recent file backup. If file backup is unavailable, faulty or not updated, Mac Recovery applications offer the solution.

You may get following error message while checking your drive with Disk Utility or fsck command line utility:

"Missing extent"

The error message suggests that these repair utilities can´t correct the issue.

Cause

Missing extent error message implies loss of file extents. There is a record to keep track of total number of extents for a file. But when the actual number of extents is found lower than expected, the above error message generates and the file or its part gets lost.

Solution

When this error message displays, you may also see a number, which is actually its inode number. Inode helps locating the file on hard disk. So, you can determine the affected file. The file can be a data file or system file.

For recovering data file, there are two options available:

• Recent file backup

• Third party Data Recovery Mac tools

You can attain system file recover using BOM.

• BOM stands for Bill Of Materials. It is used by Mac OS X installer to know about files required to be removed, installed or upgraded.

However if file backup is available and you can restore the missing information, you can follow either of these solutions to work for error message problem:

• Backup all the possible data, erase the affected volume and reinstall Mac OS X

• For Mac OS X 10.4.2 and later volumes, you can use Disk Utility or fsck

• Third party disk repair applications can also be used

In case of file backup errors or absence, use Mac Recovery tools to recover lost file. These specific applications scan the drive for recovering data.

Stellar Phoenix Macintosh Data Recovery is the robust tool to recover lost data. It is a read-only application with rich support of Data Recovery Mac features. The application supports Mac OS X 10.5.x, 10.4.x and 10.3.9. It recovers data in all possible data loss case. The application is compatible with HFSX, HFS+, HFS Wrapper, HFS and FAT file systems.