iMac and Mac mini that uses a fusion drive technology that provides a better user experience within your means. You get the benefit of SSD that is quick in loading macOS and HDD that has several gigabytes of storage space. Plus, the seamless integration (fusion) of the two drives as a single logical volume lets you work on your Mac smoothly.

However, sometimes, the fusion drive won’t show up as a single entity in Finder and appear as two separate drives due to splitting. Or, one of the two storage devices in the fusion drive may turn inaccessible due to file system corruption or drive failure. So—when the SSD is perfect—your Mac boots up, but the hard drive may not be visible in Disk Utility or may not show up in Storage under System Information. And, when the SSD is inaccessible, your Mac won’t start. 

Don’t worry. Read on to learn various troubleshooting techniques to fix Apple fusion drive not visible issue on your Mac. And, in case of any data loss, use the Mac data recovery software downloaded earlier to recover lost, deleted, or inaccessible data from your fusion drive on Mac running on macOS Big Sur or earlier.

1. Check Whether Your Fusion Drive Is Okay

To know the status of your fusion drive, perform the following steps:

a) Go to Apple menu > About This Mac. Click the Storage tab.

b) If a drive labelled as Fusion Drive is present, then it is okay. Close the window.

In case you find two separate drives, then read the next troubleshooting method.

2. Fuse the Split Drives into a Single Logical Volume

When the fusion drive is split into two separate drives (HDD and SSD), you need to fuse the two drives into a single logical volume.

Warning: You may suffer data loss during this troubleshooting process. So, backup your Mac by using Time Machine before performing the fusion steps.

Steps to Fuse Split Drives in macOS Big Sur or earlier till macOS Mojave:

a) Restart your Mac, then press-hold Command + R keys. Release them once the Apple logo or the spinning globe appears. Your Mac boots into macOS Recovery mode.

b) Go to Utilities > Terminal. In the Terminal window, type diskutil resetFusion, then press Return. When prompted, type Yes (with a capital Y), then press Return.

c) Once over, quit Terminal. From macOS Utilities window, click Reinstall macOS, then click Continue. Follow the on-screen steps to install macOS. Your Mac restarts from the fusion drive.

Steps to Fuse Split Drives in macOS High Sierra or earlier:

a) Restart your Mac, then press and hold the Command + R keys until Apple logo or spinning globe is visible. Mac boots into macOS Recovery mode.

b) Go to Utilities > Terminal. In the Terminal window, type diskutil list, then press Return. Note down the identifiers of the two internal storage drives (SSD and HDD).

c) Type diskutil cs create Macintosh\ HD disk#1 disk#2 and press Return. Here, you must replace disk#1 and disk#2 with the correct identifier of the storage drives, as noted earlier.

d) If you get a disk unmounting error, enter diskutil unmountDisk disk#1 and press Return. Here, replace disk#1 with the first and second identifier one by one. Then, retry the previous command.

e) Type diskutil cs list and press Return. Note down the identifier next to Logical Volume Group.

f) Type diskutil cs createVolume UUID jhfs+ Macintosh\ HD 100%, then press Return. Here, you must replace the UUID with the logical volume group identifier noted earlier.

g) Quit Terminal, then from macOS Utilities window, select Reinstall macOS and click Continue. Follow the on-screen instructions to install macOS. Your Mac restarts from the fusion drive.

3. Use Target Disk Mode to Access Fusion Drive

When your Mac doesn’t boot, you can use target disk mode and another working Mac to access the affected fusion drive. Steps are as follows:

a) Connect your affected Mac and the working Mac using a Thunderbolt or FireWire cable.

b) Start your Mac, then press and hold the T key. Release it after a few seconds or when the Thunderbolt or FireWire icon appears.

c) Access the fusion drive and backup all the data to an external hard drive. Now, erase the two drives using Disk Utility.

d) Open Terminal and perform the steps mentioned before to create a fusion drive and reinstall macOS.

In case, the affected fusion drive and its data aren’t accessible through target disk mode, read the next troubleshooting method.

4. Use a Bootable Mac Data Recovery Software to Access Fusion Drive

In the absence of Time Machine backup of your Mac fusion drive or when the fusion drive isn’t accessible via target disk mode, you should use a bootable Mac data recovery software to recover your lost or inaccessible data.

The steps to recover data from the non-booting fusion drive are as follows:

a) Download and install Stellar Data Recovery Professional for Mac on a working Mac. Activate the software through the purchased license key.

b) Watch the video to access the fusion drive from the affected Mac using a bootable USB flash drive and recover data. Learn more

c) Once data recovery is over, erase, and fuse the drives, then reinstall macOS.

Conclusion

Fusion drive has both a solid-state drive and a hard disk drive that allows fast booting of your Mac and storing of a large number of files without running out of space. But, sometimes, your Apple fusion drive is not visible as a single entity; does not show up in the Disk Utility, or does not boot up your Mac. So, to make things right, you need to resolve Apple fusion drive not working issue on your Mac, as explained in this post.