I stored the important data on my external hard drive, one day, when attempting to access it and I get a message: "The disk is unreadable, do you want to initialize it now?"
If you are using the latest Mac OS X operating system, the above error message will be: "The disk you inserted was not readable by this computer with three options: Initialize, Ignore, or Eject?"
What causes "The disk is unreadble error"?
"The disk is unreadble" message usually means that the directory of the drive has become corrupted. Corruption can happen for a number of reasons:
Catalog file corruption
Internal file system errors
Disconnecting or power off the drive without unmounting it
Forcing a restart on the computer
Experiencing a software lockup while writing to the drive
Turning the computer off without doing a proper shut down
Recover data from unreadble hard drive before fixing "The disk is unreadble" error
Due to the above causes, Mac Operating System fails to read the hard drive and the data stored in it becomes inaccessible. To access the hard drive again, maybe you want to run First Aid in Disk Utility. If you are experiencing the disk is unreadable error and you have a backup of your data elsewhere, use the Disk Utility to erase the drive and then restore your data from backup. If you do not have a backup, you need to use a professional Mac data recovery software to restore data.
What's worse, when encountering "The disk is unreadble error", you clicked "Initialzie" button to initialize the unreadble disk without knowing this operation would completely delete all your precious data from the hard drive, then in that case it is hard to recover lost data. So you need a professional Mac data recovery software.