Connected iMac unmountable to MacBook Pro

You're welcome.

So the partition map has become corrupted for some reason. Your first instinct to reformat the drive was right on target, but as you know that does mean that everything on the drive will be wiped. Still have a couple things to try here.

Run First Aid several times in succession on the drive. Apple recommends repairing volumes first, then containers and then the drive. So... the volumes Macintosh HD - Data, then Macintosh HD, then the container and finally the drive device. Do this and see if there is any change in the end result.

How to repair a Mac disk with Disk Utility – Apple Support (AU)

If that doesn't fix things, try booting in Single User mode and run the FSCK command. It's a file system repair command. Boot the computer while pressing Command-S. When the Mac has booted into the terminal, type the following (noting the space) and press Enter:

/sbin/fsck -fy

You may have to run that several times until you get the "Volume Okay" response.

Then run:

/sbin/mount -uw

and finally:

exit

If fsck doesn't work then a third party drive repair utility may be needed. I've used Alsoft's Disk Warrior in the past. Maybe someone else can recommend another (?).

Otherwise, erasing and reloading the drive will be the way to correct this.

Also, I'd now question why this happened. So after you regain access to the drive I would recommend using DriveDX from Binary Fruit to evaluate the overall health of the device. Maybe consider replacing it with an external startup drive.

A_Millsy wrote:

Thankyou so much for your help!

...

Is something like the Alsoft my next move?

Any other thoughts? would the apple genius bar be able to do anything?

You're welcome.

Disk Warrior maybe worth a shot. Of course you'll have to boot from an external drive so you can download and install the Disk Warrior application. Then you may be able to run the app against the drive, assuming DW can work with a drive that won't mount.

The Apple Genius bar could probably evaluate the problem and maybe give you a repair estimate.

You can make a Genius Bar appointment for hardware/software service and support using this link –

Contact Apple for support and service - Apple Support

I do notice that neither the hdd nor ssd appears to have any discoverable volume or partition. If they did you'd see a disclosure triangle next to the media name as you do see with the Apple disk image below them.

I'm afraid den.thed may be right about the fusion drive having been split, so at this point it's unlikely that data can be recovered.

The drive is failing or has failed.

A drive that is unmountable is just that... it cannot be mounted by the OS for access to the files it contains.

If you can boot the Mac in Recovery mode (Control-R at startup) then you might be able to run Disk Utility's First Aid routines on the drive to correct a fixable problem. If you cannot coax the computer to boot into recovery then a visit to a service center may be on the agenda.

Use macOS Recovery on an Intel-based Mac - Apple Support

Sadly that looks like a failed or split Fusion drive, which presents a different set of problems.

I say that because I see two Internal drives, an Apple SSD and an Apple HDD.

What does Disk Utility report when you run First Aid on the Apple HDD..?

If it is indeed a Split Fusion drive and/or one drive has failed, then it is too late to backup or recover your data.

I say that because everything will be wiped if the drives are healthy enough to be refused.

see > How to fix a split Fusion Drive - Apple Support

You should however work thru everything that D.I. Johnson suggested, before trying to refuse the split Fusion Drive.

Fusion drive. Ugh.

Good catch. (I hate those things. 🙄)

Yea' a real pain in the ars when something goes wrong.