I'm trying to create a small FAT32 partition which I can use to transfer files between my Macintosh HD partition and the Windows Bootcamp partition on my Mac.

I'm using Big Sur. I've gone to Disk Utility and clicked 'partition' when 'Fusion Drive' is selected on the left.

This is the screen I get: Disk Utility screenshot

When FAT32 or ExFat is selected as the new partition format, I am unable to change the size of the volume. It's stuck at 360GB, and I only want 1GB.

I don't want to play around with this without understanding it, because it's dangerous.

Does anyone know what I need to do to be able to create a smaller partition?


My model of mac: iMac 2019.

Output of 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         878.0 GB   disk0s2
   3:       Microsoft Basic Data ⁨BOOTCAMP⁩                122.0 GB   disk0s3

/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         27.6 GB    disk1s2

/dev/disk2 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +905.6 GB   disk2
                                 Physical Stores disk1s2, disk0s2
   1:                APFS Volume ⁨Macintosh HD⁩            18.5 GB    disk2s1
   2:              APFS Snapshot ⁨com.apple.os.update-...⁩ 18.5 GB    disk2s1s1
   3:                APFS Volume ⁨Macintosh HD - Data⁩     520.7 GB   disk2s2
   4:                APFS Volume ⁨Preboot⁩                 397.5 MB   disk2s3
   5:                APFS Volume ⁨Recovery⁩                626.4 MB   disk2s4
   6:                APFS Volume ⁨VM⁩                      2.1 GB     disk2s5

/dev/disk3 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *1.0 TB     disk3
   1:               Windows_NTFS ⁨TOSHIBA NEW⁩             1.0 TB     disk3s1
  • 1
    Add to your question the the model/year of your Mac and the output from the command diskutil list. Feb 22, 2022 at 21:19
  • diskutil apfs resizecontainer disk0s2 876.9G fat32 MYFAT 0 Feb 23, 2022 at 14:42

2 Answers 2


I created a new partition with the disk utility in the desired size (32GB) and formatted it in the Mac OS Extended format. After that I deleted this partition and changed the format to FAT32.

  • 1
    How is it possible to change a partition’s format after it is deleted, if this is what you are suggesting? In addition, the OP owner has apparently a fusion drive. Is the solution you are suggesting valid for a fusion drive?
    – Alper
    Oct 7, 2022 at 14:53

After switching the setting to FAT32 you can only change the size using the pie chart on the left. Click on the edge of the big circle where the small grey circle is and do a click-and-drag to set it to the desired size.

Note, if you type in a size before switching to FAT32 then it will reset the size when you change to FAT32.

No idea why they disabled typing in the size for FAT32. Seems bizarre.

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