Mac Mini drive mount error in Target Disk Mode (-119930868

Question

Level 1

4 points

Mac Mini drive mount error in Target Disk Mode (-119930868

I have a Mac Mini that recently had booting problems. Upon further inspection through Recovery Mode, it seems like the hard drive encountered a key index out of order error, and is failing to boot normally. I can still open a terminal and navigate through the folders.

I then went to my iMac, connected the Mac Mini through a Thunderbolt 4 cable, and booted the Mac Mini to Target Disk Mode by holding "T" as it boots. The Mac Mini gets recognised under the Thunderbolt 4 Bus, and I can see it in Disk Utility, however, I'm having trouble mounting it, and I get this error when I try and mount it.

Could not mount “AppleAPFSMedia”. (com.apple.DiskManagement.disenter error -119930868.)

Here is a screenshot:

Here is the output of the command diskutil list external:

 diskutil  list  external

/dev/disk2 (external):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                         500.3 GB   disk2
   1:                        EFI EFI                     314.6 MB   disk2s1
   2:                 Apple_APFS Container disk3         365.0 GB   disk2s2

/dev/disk3 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +365.0 GB   disk3
                                 Physical Store disk2s2
   1:                APFS Volume                         12.4 GB    disk3s1
   2:                APFS Volume Macintosh HD - Data     323.5 GB   disk3s2
   3:                APFS Volume Preboot                 4.7 GB     disk3s3
   4:                APFS Volume Recovery                1.3 GB     disk3s4
   5:                APFS Volume VM                      24.6 KB    disk3s5
   6:                APFS Volume Update                  72.9 MB    disk3s6

/dev/disk4 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk4
   1:       Microsoft Basic Data EXTREMESSD              500.1 GB   disk4s1

And here is the output of the command diskutil ap list:

(see additional text)

I also tried diskutil mount readOnly disk3s1, which gave this output:

diskutil  mount  readOnly disk3s1
Volume on disk3s1 failed to mount
Perhaps the operation is not supported (kDAReturnUnsupported)
This appears to be an APFS Volume; note that locked APFS volumes
will not mount unless unlocked (e.g. "diskutil apfs unlockVolume")

None of the volumes are locked and/or encrypted.

Note that both the Mac Mini and iMac are Intel-based Macs. The iMac runs on 10.15.7, and the Mac Mini runs on a more updated OS since I updated that a couple months ago.

Is there a way for me to be able to fix this issue and mount the Mac Mini as intended? I want to backup and recover the files before I reformat the Mac Mini. I know I can just go to recovery mode and use the terminal to copy the files to an external drive, but doing it with a UI gives me the peace of mind that I am not going to miss any of the important files I have in here.

[Edited by Moderator]

Posted on Aug 3, 2026 11:53 PM

Reply

Answer 1

Aug 12, 2026 8:32 PM in response to arnold_v

arnold_v wrote:

Hi, thanks for taking the time to reply.

I already tried Recovery mode, used Disk Utility, and First Aid. That's when it showed the error about the key index out of order, and the repair fails. I have looked up the error and it seems to be an unfixable error even with paid tools.

Your picture shows you are trying to mount the APFS Container. You don't mount the Container, you need to mount the actual APFS volumes within that Container which is the one labeled "Macintosh HD - Data".

If Disk Utility cannot repair the volume or Container after several attempts, then the file system cannot be repaired. Which volume contains the errors/warnings....or does the Container have the errors/warnings? Since the macOS system volume is affected here, the only option would be to erase the whole physical SSD to destroy the existing partitions & create a new partition table & APFS file system followed by reinstalling macOS & restoring the data from a backup.

FYI, the Mac Mini SSD is very low on Free storage space as well with just 22GB Free as shown in the picture of Disk Utility. That is the absolute minimum. Ideally it should have 50GB - 100GB of Free space before starting any workloads.

Plus it seems you have some missing storage on that 500GB SSD since the APFS Container is only 365GB so you are missing about 130GB on that SSD. I don't see any other partitions listed in the Terminal output, nor any deleted partitions which typically show up listed as "(free space)". This could indicate a hardware issue with this SSD.

You can check the health of the SSD by using DriveDx (free trial period)....this should be possible while the Mac Mini is connected by a Thunderbolt cable in Target Disk Mode, but never tried this configuration before that I can recall. If this doesn't work, then I can provide other options for checking the health of the Mini's SSD. I would be happy to examine the health report if you post the complete DriveDx text report here using the "Additional Text" icon which looks like a piece of paper on the forum editing toolbar.

Reply

Answer 2

den.thed

Level 10

96,750 points

Aug 4, 2026 6:48 AM in response to arnold_v

arnold_v wrote:

I have a Mac Mini that recently had booting problems. Upon further inspection through Recovery Mode, it seems like the hard drive encountered a key index out of order error, and is failing to boot normally. I can still open a terminal and navigate through the folders.

What screen does the Mac mini go to when it fails to startup...?

see > If your Mac doesn't start up all the way - Apple Support

I then went to my iMac, connected the Mac Mini through a Thunderbolt 4 cable, and booted the Mac Mini to Target Disk Mode by holding "T" as it boots. The Mac Mini gets recognised under the Thunderbolt 4 Bus, and I can see it in Disk Utility, however, I'm having trouble mounting it, and I get this error when I try and mount it.

If you are unable to unlock and access the Mac mini's drive in Target Display Mode for whatever reason.

Go back to the basics. Startup the Mac mini in macOS Recovery and use Disk Utility > First Aid.

Using the Intel directions at > How to start up from macOS Recovery - Apple Support

Is there a way for me to be able to fix this issue and mount the Mac Mini as intended? I want to backup and recover the files before I reformat the Mac Mini. I know I can just go to recovery mode and use the terminal to copy the files to an external drive, but doing it with a UI gives me the peace of mind that I am not going to miss any of the important files I have in here.

If you do not have a viable backup and can not get the Mac mini to startup...?

Then this sounds like the best way to try and recover your data.

Reply

Answer 3

arnold_v Author

Level 1

4 points

Aug 4, 2026 12:15 PM in response to den.thed

Hi, thanks for taking the time to reply.

I already tried Recovery mode, used Disk Utility, and First Aid. That's when it showed the error about the key index out of order, and the repair fails. I have looked up the error and it seems to be an unfixable error even with paid tools.

Reply

Answer 4

OldToad

Level 3

521 points

Aug 10, 2026 11:46 AM in response to arnold_v

Have you tried the following: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and text again.

Note: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will assure a successful boot into Safe Mode.

It may be a bit slower in booting as it's performing the following:

- Prevents certain software from loading as your Mac starts up. This includes login items and extensions that aren't required by macOS, and fonts that weren't installed by macOS.
- Performs a basic check of your startup disk, similar to the more comprehensive check performed by the First Aid feature of Disk Utility.
- Clears some system caches, including font caches and the kernel cache, which are automatically created again as needed. This can temporarily make more storage space available on your startup disk.

Reply