Wednesday, February 2, 2011

Catalog File Corruption in Mac

Catalog File is a Mac system file that is used by HFS (Hierarchical File System) File Manager to keep information about hierarchy of the files and directories on Mac volume.

The catalog file is ordered as B-tree file and thus consists of header node, leaf nodes, index nodes and map nodes (if necessary). The allocation block number of first file extent of catalog file is stored in Master Directory Block or MDB.

When you mount the volume, the stored information is copied in the volume control block of that volume. From header volume, File Manager could access node number of the root node of catalog file and from root node, File Manage could find whole catalog file.

A unique CNID (Catalog Node ID) is assigned to the every node of catalog file. For files CNID is file ID and for directories its directory ID. For a given directory or file, the parent ID is CNID of parent directory. When operating system accesses files or data from HFS file system volume, it first interacts to the catalog file and gathers complete information about the hierarchy.

But sometimes when you try to access data from your hard drive, you may get an error message similar to the following:

“Verifying volume
Checking HFS Plus volume.
Invalid record count
Invalid record count
Catalog file entry not found for extent
The volume needs to be repaired.”

After this error message, you can not access data from Mac volume and thus face the critical situations of data loss.

You may encounter this problem because of corruption to the catalog file. Due to same, operating system can not file the required information to read data from volume. To fix this problem, you need to go for Mac Data Recovery. You can carry out Mac Data Recovery in an easy and straightforward way using third party Mac Recovery software.

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