iMac 2017 1 TB HDD 28 GB SSD Fusion Drive

Recently, I decided to do a clean install with diskutil erasedisk, reformatting through disk utility, and resetting the Fusion Drive to wipe everything after messing with my GPT in an attempt to recover a partition. With the clean install, I upgraded from macOS High Sierra to macOS Monterey which converted my MacOS Extended Fusion drive to APFS and no issues occurred. Then, I decided to run Boot Camp and encountered a 0x80070070 error during the final Windows installation. So, I redid the Boot Camp process, but this time I noticed two things. First, the Disk Utility showed an excess amount of unremovable "free space" in the partition menu after Boot Camp restored the partition. Removing the free space partition just results in a to small error, since it would equal 2 TB total (greater than my actual storage size). The APFS container and the volumes within all show the excessive free space. The excess free space does not show up on the Disk Utility in recovery mode.

Free Space: 972 GB Macintosh HD: 1.03 TB

Second, I could not get Windows during the installation process since it states the following.

Windows cannot locate the disk and partition specified in the unattended answer file's setting. Make sure the settings references a valid partition and restart the partition

Using first aid in Disk Utility, I get a warning: MT Mapping is not fully referenced.

I tried doing a clean install again which resolved the warning, but the Disk Utility still shows an excess amount of free space.

Based on what I observed, eraseDisk and reformatting does seem to make the free space issue disappear, as long as the partitions are not messed with later on by a software or person. However, I suspect it might be some sort of GPT corruption or an APFS issue exacerbated by the Fusion Drive. I do not have much knowledge on this particular matter since this occurred recently and I do not have a backup. Verifying and repairing the disks/volumes does not fix the excess space issue either.

Any help on resolving this issue would be appreciated.

diskutil list

    /dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk0
   1:                        EFI ⁨EFI⁩                     209.7 MB   disk0s1
   2:                 Apple_APFS ⁨Container disk2⁩         1000.0 GB  disk0s2

/dev/disk1 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *28.0 GB    disk1
   1:                        EFI ⁨EFI⁩                     314.6 MB   disk1s1
   2:                 Apple_APFS ⁨Container disk2⁩         27.7 GB    disk1s2

/dev/disk2 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +1.0 TB     disk2
                                 Physical Stores disk1s2, disk0s2
   1:                APFS Volume ⁨Macintosh HD - Data⁩     4.9 GB     disk2s1
   2:                APFS Volume ⁨Preboot⁩                 268.5 MB   disk2s2
   3:                APFS Volume ⁨Recovery⁩                1.1 GB     disk2s3
   4:                APFS Volume ⁨VM⁩                      1.1 MB     disk2s4
   5:                APFS Volume ⁨Macintosh HD⁩            15.2 GB    disk2s5
   6:              APFS Snapshot ⁨com.apple.os.update-...⁩ 15.2 GB    disk2s5s1


diskutil apfs list

APFS Container (1 found)
+-- Container disk2 8A6CEABD-E62E-48F8-AF54-6D5EEABB2271
    APFS Container Reference:     disk2 (Fusion)
    Size (Capacity Ceiling):      1027680514048 B (1.0 TB)
    Capacity In Use By Volumes:   26512023552 B (26.5 GB) (2.6% used)
    Capacity Not Allocated:       1001168490496 B (1.0 TB) (97.4% free)
    +-< Physical Store disk1s2 466C5860-31D6-4654-BD3E-E98C7E5B0FC0
    |   -----------------------------------------------------------
    |   APFS Physical Store Disk:   disk1s2 (Main, "Faster" Disk Use)
    |   Size:                       27685384192 B (27.7 GB)
    +-< Physical Store disk0s2 53437EAE-B2D3-44BD-95A8-722A3391A600
    |   -----------------------------------------------------------
    |   APFS Physical Store Disk:   disk0s2 (Secondary, Designated Aux Use)
    |   Size:                       999995129856 B (1000.0 GB)
    +-> Volume disk2s1 87D077E6-7A84-4699-A9AA-D432B9373FBE
    |   ---------------------------------------------------
    |   APFS Volume Disk (Role):   disk2s1 (Data)
    |   Name:                      Macintosh HD - Data (Case-insensitive)
    |   Mount Point:               /System/Volumes/Data
    |   Capacity Consumed:         5433786368 B (5.4 GB)
    |   Sealed:                    No
    |   FileVault:                 No
    +-> Volume disk2s2 2DA20AB8-C894-404F-A897-DFE03DADA601
    |   ---------------------------------------------------
    |   APFS Volume Disk (Role):   disk2s2 (Preboot)
    |   Name:                      Preboot (Case-insensitive)
    |   Mount Point:               /System/Volumes/Preboot
    |   Capacity Consumed:         268513280 B (268.5 MB)
    |   Sealed:                    No
    |   FileVault:                 No
    +-> Volume disk2s3 6EC9F12E-F1A6-4C30-83DB-70A40DBC01B8
    |   ---------------------------------------------------
    |   APFS Volume Disk (Role):   disk2s3 (Recovery)
    |   Name:                      Recovery (Case-insensitive)
    |   Mount Point:               Not Mounted
    |   Capacity Consumed:         1109127168 B (1.1 GB)
    |   Sealed:                    No
    |   FileVault:                 No
    +-> Volume disk2s4 1BA6A158-2131-4844-B1B6-ED2719419B78
    |   ---------------------------------------------------
    |   APFS Volume Disk (Role):   disk2s4 (VM)
    |   Name:                      VM (Case-insensitive)
    |   Mount Point:               /System/Volumes/VM
    |   Capacity Consumed:         1069056 B (1.1 MB)
    |   Sealed:                    No
    |   FileVault:                 No
    +-> Volume disk2s5 1680A026-202C-40D2-85CB-BCC42D7B3211
        APFS Volume Disk (Role):   disk2s5 (System)
        Name:                      Macintosh HD (Case-insensitive)
        Mount Point:               Not Mounted
        Capacity Consumed:         15183765504 B (15.2 GB)
        Sealed:                    Yes
        FileVault:                 No
        Snapshot:                  21DAE8E2-71B4-4EA0-AB39-C709E6F73C05
        Snapshot Disk:             disk2s5s1
        Snapshot Mount Point:      /
        Snapshot Sealed:           Yes

df -h

Filesystem       Size   Used  Avail Capacity   iused      ifree %iused  Mounted on
/dev/disk2s5s1  957Gi   14Gi  933Gi     2%    500632 4293967565    0%   /
devfs           190Ki  190Ki    0Bi   100%       658          0  100%   /dev
/dev/disk2s4    957Gi  1.0Mi  933Gi     1%         1 9779973520    0%   /System/Volumes/VM
/dev/disk2s2    957Gi  256Mi  933Gi     1%       723 9779973520    0%   /System/Volumes/Preboot
/dev/disk2s6    957Gi  668Ki  933Gi     1%        19 9779973520    0%   /System/Volumes/Update
/dev/disk2s1    957Gi  4.8Gi  933Gi     1%    107788 9779973520    0%   /System/Volumes/Data
map auto_home     0Bi    0Bi    0Bi   100%         0          0  100%   /System/Volumes/Data/home

gpt -r show disk0

gpt -r show disk0
     start            size    index   contents
         0               1            PMBR
         1               1            Pri GPT header
         2              32            Pri GPT Table
        34               6                 
        40          409600        1   GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
    409640      1953115488        2   GPT part - 7C3457EF-0000-11AA-AA11-00306543ECAC
1953525128               7
1953525135              32            Sec GPT table
1953525167               1            Sec GPT header

gpt -r show disk1

gpt -r show disk1
     start            size    index   contents
         0               1            PMBR
         1               1            Pri GPT header
         2               4            Pri GPT Table     
         6           76800        1   GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
     76806         6759127        2   GPT part - 7C3457EF-0000-11AA-AA11-00306543ECAC
   6835933               4            Sec GPT table
   6835937               1            Sec GPT header


Disk Utility Free Space in container and removing said free space.  View of Container and Partition Mapping

Result of attempting to removing "free space"  Result of removing "free space"

View of Fusion Drive View Of Fusion Drive and Partition Mapping

  • Might be helpful if you explicitly stated what does not add up. Mar 28 at 2:11
  • Hi, I updated the title and added pictures to give better insight. I'm just not sure why there's an additional 972GB of free space on top of the 1.03TB formatted partition. In the container and volumes it shows extra unallocated free space however the fusion drive just shows the 1.03TB partition.
    – Dan
    Mar 28 at 3:28
  • At first, I could not see where you were getting the value of 972 GB. I found the value in an image you posted of the Disk Utility. When the Disk Utility shows strange results, you should quit the Disk Utility and then open the Disk Utility. If you did not do this, then you should expect the images you posted from Disk Utility to contain inaccurate results. This problem has existed for decades with Apple showing no signs they wish to repair the problem. Mar 28 at 5:30


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