For a Mac user, disk problems such as disk corruption or drive errors may lead you to initialize your disk. This can lead apparently to the loss of all data on that drive. Drive formatting and partition table changes also seem to cause data to vanish. It's not gone-here's what to do.
What to Do if Your Disk Is Initialized
If you connect a disk to your Mac, such as an external hard drive, you may be prompted with a screen asking you to initialize the disk. Whether you realize that this is not the correct course of action or not, you might initialize the disk. If you do, you may believe that the data is gone. It appears gone because you can no longer see the partitions, folders, or files.
You will be prompted after initializing the disk to reformat the drive. At this point you may realize the problem and choose not to format the disk, and begin wondering how you will get your files back. At this point they are inaccessible, but don't think all is lost--the contents of the drive have not been overwritten--there is still hope.
Disk First Aid Fails
You may have encountered problems before if you tried running Disk First Aid at this point. If you're reading this, it's likely that Disk First Aid failed, and you probably saw some error messages that provided more questions than answers. What you may need at this point is a program that can look directly at the contents of the drive at a low level, reading blocks on the disk without using the I/O processes used by the OS X operating system.
After all, the OS can't read what we know is on the drive, and the OS disk repair software has failed. The utility programs that work here use direct access and block reading methods to read the data from the drive and reconstruct the file, folder, volume, and partition data that is present, but which has problems being interpreted by the OS.
Partition Table Problems or Catalog Corruption
Recovering lost files on disks and drives with problems is often simply a problem with a deleted, changed, damaged, or corrupt partition table. If the table does not have the proper data, the volumes are not seen by the OS X file system interface. The files are still present in most of these cases, you simply need to read them directly as we have described. A multi-purpose utility for lost data access such as Mac Data Recovery from Disk Doctors is a tool to recover from these sorts of problems.
Utilities like this read directly from the data on the drive, and use scanning methods to read and rebuild the partition or volumes. Even if the XFS+ or HFSX catalog is corrupt the program can extract data or fix the disk.
For more information on a great utility to restore your initialized disk, take a look at my review of Disk Doctors Mac Data Recovery software for Apple Mac OS X 10.4 and higher.