GDisk usage on a Macintosh

Although this is a LINUX forum I hope the info is cross platform in its usage. Not sure how to categorise this topic

My issue history
I have had a issue with an old hard drive that I used to boot from externally as my work drive on my Mac. While trying to get some data off this drive over a few days, the drive suddenly would not wake up from sleep (let sit overnight) so I powered off the computer and then back on. The drive would no longer show up on the desktop never mind boot. Tried Apple disk utility to no avail, did not show the proper partitions on the drive either. Tried a number of drive utilities to no avail so I have tried gdisk to see I could recapture the partitions and get the drive to boot again. Well, the issue there is simply, unless you know the partition details it likely won’t work. Went as far as to use TestDisk to recover the data as best as it could. Although I did get some back it was not totally complete. Knowing I am caught between a rock and a hard place I knew I was not going to be successful. I have formatted the hard drive and was trying to learn a bit about the use of gdisk and creating partitions on the device. Problem I run into is the partitions are created and I can see them in Apple disk utility, they just are grey’d out and not available to use until I formatted them.

So, although this is a long read for a question, how do you create the partitions so a Mac can read them and work without the need to format? If I knew the proper partition configuration should have I been able to get the drive bootable (might be a tough question to answer I admit) from the initial problem.

I certainly have learned that I don’t know very much about hard drives and the OS’s on them, the way they work. Especially now that Apple has the newer APFS file system. People say its impossible to “fix” this system when it fails. I think the HD was HFS+ but not totally sure at this point. Anyway, I know this is a linux site but I am hoping you might be able to answer as its difficult to get a forum for gdisk to pose questions.

Thanks in advance

You’ll likely find people with a similar problem and possible solution here. See also this.

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