Unable to mount External HD - Mac OS Extended
There are several approaches you can take to this.
-
Fix the drive using better tools than fsck. DiskWarrior has always been the go-to tool for this. It will not damage the drive further, as it makes 'virtual' fixes which you can test before committing the changes. Disk Warrior is great on HFS+ but cannot handle APFS.
-
Rescue the drive to another drive. Disk Drill is a good tool for this. It will scavenge the drive for any undamaged data then allow you to copy that off to another drive. This should also leave the original unchanged.
-
Copy the data off, as is & try to recover once you know you have a copy. Using the built-in
ddcommand to literally copy all data, byte for byte across to another drive. Instructions at My External Hard Drive's format changed to FAT16 without any reason
This still requires you to perform the rescue using Disk Drill or similar, but working on a safety copy. -
Give the drive to a data rescue professional.