Can't erase Fusion drive on my 2015 iMac

[212rikanmofo]

My iMac was working fine until today I got the beachball of death and it took a long time, so I had to manually shut down my computer. Upon restarting it, I get a screen with a circle and a line going through it. I tried to restart my mac again using CMD+R to get into recovery mode, and went into Disk Util, and it showed my Macintosh HD as red, it ask to fix or ignore. So I click on fix thinking it would fix it, but instead it formats my entire drive. All 3TB of information gone. Sigh... I lost everything.

And now I can't even reinstall Mac OS because it Disk Util keeps telling me it can't unmount my drive. I am trying to erase it. Does anyone know how to fix this? I've had such a terrible day because of this. I already did very permissions and repair in disk util and it shows everything as being okay. So I'm not sure why I can't even format my drive, it keeps saying unable to unmount. Prior to this my drive was unmounted so I'm not sure what the deal is.

I heard some people telling me that I can force unmount it, but how can I do this when I don't have an operating system anymore?

Please help anyone.

 

[mreg376]

Sounds like a failed drive, although 2015 is pretty recent for that.

 

[212rikanmofo]

I really hope its not a failed drive, this looks like a difficult job to replace it. Having to remove the screen and all. I really don't want to take it to an authorized Apple center just to replace a drive.

I tried reinstalling Mac OS three times, and it gave me an error every time when it was about 2 minutes remaining left. Is there anyway I can tell if the Fusion drive failed for sure?

It has a 128GB SSD + 3TB HDD.

If I were to replace that, can I just replace the HDD or do I have to replace the entire thing with another Fusion drive or can I just swap it out entirely for an HDD instead?

UPDATE: I was able to erase/reformat the drive and did a repair and verify drive and it seemed okay, it had some errors but it fixed those. Is there a command to check the STATUS or Health of your drives to know for sure? But everytime I try to reinstall the OS, at the end it keeps failing saying error while trying to prepare installation. I don't understand. My drive status seems okay.

Also whats the difference between the Recovery modes CMD+R and CMD+OPTION+R? I notice the former has an older interface and when you select reinstall OS it gives Mountain Lion 10.8, but if you boot with CMD+OPTION+R it gives you Mac OS High Sierra instead? Confused about those 2 recovery modes.

 

[mreg376]

I'm assuming your iMac is out of warranty, yet it might be worth a trip to the Genius Bar anyway for a definitive diagnosis. You probably spent a good amount on your iMac and I'm not sure you want to spend time playing around its innards. Replacement of the drive should not be a very expensive proposition, and unless you need that much storage on board you may want to consider a 256 or 512GB SSD and external storage for more reliability.