WD single 4 TB Green ExFAT drive JBOD in WD My Book Thunderbolt Duo not mounting in Mac anymore

Hi, I own a   WD My Book Thunderbolt Duo and I recently upgraded the drives inside of it to 8 TB (two single 4 TB WD green drives). Both WD drives are formatted ExFAT and set to Individual Drives (JBOD) via WD Drive Utilities.

I use iMac with Mac OS X 10.9.3 Mavericks.

The problem happened today, one of my new 4 TB drives only being 1 week old with data on it, stop mounting -not showing up. I can only see the drive in Disk Utility, but the unfunctioning drive is now renamed to “disk2s2” and the format says “MS-DOS (FAT)”. I tried the “Repair Disk” option, and get the following message:

Verify and Repair volume “disk2s2” Checking file system** /dev/disk2s2

Invalid sector size: 0

Volume repair complete.Updating boot support partitions for the volume as required. Error: Disk Utility can’t repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files.


I really need the unfunctioning drive to mount/work as I have my life’s work on it! The other 4 TB drive in the other bay of the   WD My Book Thunderbolt Duo slot still works, it shows up mounted.

What I’ve done so far:

  • Called WD Tech support; no help, but simple -power off, takeout and reinsert drives into bay

  • Pulled unfunctioning drive from Bay A and inserted into Bay B; same problem, drive does not mount

  • Pulled unfunctioning drive and installed into 3rd party external enclosure and hooked it up to iMac and Windows machine; still not mounting

  • Changed the thunderbolt cables with new thunderbolt cables; still not mounting

Please does someone know any best practices to get my unfunctioning drive to mount again!


Unfortunately it seems the partition on the drive may be corrupted. formatting the drive will probably make it work again but you say you have information on the drive that you don’t want to loose.

I recommend trying to recover the data using a data recovery software. There are several kinds of Data Recovery software available. If you do a  web search for  Data Recovery  it will yield plenty of data recovery software options.