New and unformatted Mac hard drive need to be initialized before using it to create a partition for organizing the storage space and making it accessible by the macOS High Sierra. Also, you have to initialize your brand new hard drive when it does not show up even after connecting it to your Mac.
Initializing a Mac hard drive builds partition table and creates new partitions which can further be formatted to create a new file system. Initializing a Mac drive (that contains data) erases all the content; therefore, before initializing it, make sure to take a backup of all your data.
Certainly backing up, let’s say 4 TB of valuable data is indeed a super time-consuming process impractical on a regular basis, so the probability of having an updated backup is near zero.
If you have unintentionally initialized your Mac hard drive, you can recover data from it using Stellar Mac Data Recovery Professional. Its intuitive interface and robust features make it easier to recover lost files and folders from the initialized drive. Further, some deleted files are not easy to recover and require a bit more digging, this is when the Deep Scan feature of the software comes in handy. It searches every available sector of the initialized drive to find traces of missing data.
Here is how you can recover data from initialized Mac drive:
After recovering data from the initialized Mac hard drive, you can re-format the drive through Disk Utility and use the drive again.