I have been using the below said HDD with my Macbook and Windows (8.1 Pro) machine interchangeably for over an year. Since the HDD is NTFS formatted I use Tuxera NTFS drivers to enable write on Macbook, which worked fine unless one fine day on plugging in the HDD to my Macbook I find the HDD to be completely empty. On firing disk utility I come to know that hard drive has been formatted to Mac OS Extended partition type. Please note this happened instantaneously as soon as I plugged in the machine to my Macbook, so I assume the drive was not actually formatted but some sort of partition format change has happened. After this I was unable to access any data on the drive on my Macbook and the drive was not being detected on the Windows machine since I do not have 3rd party tools to read Mac OX extended partition on Windows. I have tried FileSalvage data recovery tool to Salvage (Raw Recovery) files from the same drive and able to recover the content but lost the directory structure and file properties. Due to the nature of data stored on the drive (Datasets, Source Code, Resources in Zip files) I would really like to get back my directory structure. Since no actual format happened on the drive (Reason 1 - The format type flip was instantaneous, Reason 2 - Recovered data is still in good shape) I would really like to know if I can convert the Mac OS Extended formatted drive back to NTFS and recover directory structure along with data as it was before that unfortunate day when my machine suddenly decided to format my drive without permission. System - MacBook Air (13-inch Mid 2013), OS X Yosemite (10.10.3) Product (with issues) - WD My Book Studio II - 4 TB (NTFS Formatted using Tuxera NTFS for Mac STABLE VERSION 2013.2) PS: I tried reproducing the scenario on another Seagate 4TB drive (NTFS formatted) with dummy data and after few weeks of random hit and trials I was able to replicate the issue and the drive was flipped to Mac OS Extended format again. I removed the Tuxera NTFS drivers after that suspecting that's causing the issue and since then nothing has happened to my NTFS drives on Macbook. The 2nd Seagate HDD is available for testing the solutions to resolve the issue with original WD HDD.