How to recover lost data from unmounted drive on macOS/Mac OS X?
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 lost data from unmounted drive on macOS?
It is a common problem that can cause data loss after external hard drive is unmountable and disk utility fails to repair unmounted drive. If the Mac hard drive volume fails to mount and becomes inaccessible, the best way to overcome this problem is to recover lost data from unmounted drive. This article will analyze the reason and let you know how to recover lost data from unmounted 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 lost data from unmountable Mac hard drive volume
M3 Mac Data Recovery is the professional Mac data recovery software which can recover lost data from unmountable Mac hard drive volume, external hard drive, USB drive, flash drive, etc. in macOS Catalina 10.15/Mojave 10.14/High Sierra 10.13/10.12 and Mac OSX 10.11/10.10/10.9/10.8 and supports HFS, HFS+, exFAT and FAT32 file systems.
Tutorial to recover data from unmounted 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 unmountable Mac hard drive or volume.
Step 3: M3 Mac Data Recovery is scanning lost data from unmountable hard drive.
Step 4: After data is found, please select them and click Recover to start data recovery 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.