[Solved] How to recover data from unmountable Mac hard drive volume?

I plugged my 3TB USB external hard drive into my MacBook Air and it did not mount. When I ran the Disk Utility, the hard drive was visible, but the volume was unmountable and unrepairable. The major error is invalid b-tree node size. How should I recover data from unmountable drive in Mac OS X?

External hard drive not mounted in disk utility

It is a common problem that can cause data loss after external hard drive is unmountable and disk utility fails to repair unmountable drive. If the Mac hard drive volume fails to mount and becomes inaccessible, the best way to overcome this problem is to recover data from unmountable drive. This article will analyze the reason and let you know how to recover data from unmountable drive under Mac computer.

Why Mac hard drive volume fails to mount?

There are several common reasons which cause Mac hard drive volume fails to mount:

File system corruption - Mac OS X fails to access volume data if the local file system structure is corrupted. Usually, file system becomes corrupted after improper file system conversion, erroneous formatting/re-formatting operations, etc.

Volume header corruption - Volume header is very important to provide necessary information to the OS. It uses header information to mount particular volume. When volume header is corrupted, volume will be unmountable.

Disk Utility failure - While performing resizing, re-partitioning, file system conversion etc. using a Disk Utility tool, even a small error could result in unmontable Mac hard drive volume.

Log file corruption - If the log file or directory structure is altered or damaged, it will make particular volume be inaccessible or unmountable.

Bad sectors on hard drive, OS malfunction, sudden system reboot, etc. also cause Mac hard drive volume to become unmountable. However, you can avoid data loss after any unexpected data crisis using a professional Mac data recovery software. After data recovery is done successfully, use the disk utility to format the unmountable Mac hard drive volume, then it will be working again.

Recover data from unmountable Mac hard drive volume

M3 Mac Data Recovery is the professional Mac data recovery software which can recover data from unmountable Mac hard drive volume, external hard drive, USB drive, flash drive, etc. in macOS 10.12 and Mac OSX 10.11/10.10/10.9/10.8/10.7/10.6 and supports HFS, HFS+, exFAT and FAT32 file systems.

Tutorial to recover data from unmountable drive with M3 Mac Data Recovery

Step 1: Download, install and then launch M3 Mac Data Recovery on your Mac computer.

Step 2: Please select "In a specific volume" option and then choose unmountable Mac hard drive volume from the drop-down volume list or select "In a specific hard drive" and then choose unmountable hard drive from the drop-down hard drive list.

Free Mac data recovery software

Step 3: M3 Mac Data Recovery is scanning lost data from unmountable hard drive.

Scan the lost data from unmountable Mac hard drive volume

Step 4: After data is found, please select them and click Recover to start data recovery from unmountable Mac hard drive volume.

Recover data from unmountable Mac hard drive volume

Format unmountable Mac hard drive volume

After data recovery is successfully done, please reformat the unmountable Mac hard drive volume, then it will be working again.

Step 1: Launch Disk Utility from Utilities.

Step 2: Click the icon for your hard drive in the sidebar on the left.

Step 3: Click the Erase tab along the top of the window and enter the related information.

Step 4: Click the Erase button to start format operation.

Related Mac data recovery solution: