What Is The Smallest Partition I Can Use Disk Utility to Add

disk-utilitypartitionssd

I'm trying to add a new partition to my Macbook, in order to dual boot with Linux. I have a 250GB drive, with 70GB free. However when I try to use Disk Utility it says
"This volume can not be split because the resulting volumes would be too small."

This answer tells someone having the same problem their drive is simply too small. Can I really not create a 70GB partition? What is the smallest size I would be able to create?

Best Answer

While the Disk Utility application is move convenient than using the diskutil command, often the Disk Utility does not provide sufficient support for non-Apple related tasks. Adding Linux definitely falls into this category. The amount you can shrink a APFS container can found by using the diskutil command. For example, I have a APFS container on my external drive. Below is the partial output from from the command diskutil list. This shows the partitions on my external HDD.

/dev/disk3 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *400.1 GB   disk3
   1:                        EFI EFI                     209.7 MB   disk3s1
   2:         Microsoft Reserved                         16.8 MB    disk3s2
   3:       Microsoft Basic Data BOOTCAMP                125.7 GB   disk3s3
   4:       Microsoft Basic Data WINSTALL                11.5 GB    disk3s4
   5:           Windows Recovery                         629.1 MB   disk3s5
   6:                 Apple_APFS Container disk4         200.0 GB   disk3s6
   7:                  Apple_HFS BU                      61.3 GB    disk3s7
   8:                  Apple_HFS Macintosh HD via rEFInd 200.0 MB   disk3s8
   9:                  Apple_HFS Preboot                 200.0 MB   disk3s9
  10:       Microsoft Basic Data BOTTOM                  57.7 MB    disk3s10

Since the APFS container has the identifier disk3s6, I can use the command shown below to determine how much the APFS container can be resized.

 diskutil apfs resizecontainer disk3s6 limits

The resulting output is shown below.

Resize limits for APFS Physical Store partition disk3s6:
  Current Physical Store partition size on map:   200.0 GB (200000000000 Bytes)
  Minimum (constrained by files/snapshots):       76.7 GB (76683403264 Bytes)
  Recommended minimum (if used with macOS):       87.4 GB (87420821504 Bytes)
  Maximum (constrained by partition map space):   200.0 GB (200000000000 Bytes)

This output shows the minimum size is 76.7 GB. The size of the smallest partition you could created after the APFS container would be hard to determine exactly. Anything reasonably small would be accepted. For example, the command below would create new empty partition of approximately 100 MB in size.

diskutil apfs resizecontainer disk3s6 199.9G %noformat% none 0

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Lion has a hidden partition which contains recovery information. Shrinking the partition, according to an Apple employee, is not supported. He hooked up my MBP to an external hard drive and wiped and reinstalled Lion in order to fix things.

In more detail, what happens is this: When you try and resize the main partition, it doesn't include the recovery partition. When you hit "Apply Changes," it does a checksum to make sure that nothing's accessing the drive. It then gets started, doing another checksum, and discovers that something's changed, breaking the previous checksum.

Cannot use Disk Utility to create partition from free space on external USB drive

I think Disk Utility misses a proper EFI partition at the beginning of the disk.

If you don't want to completely erase the drive you should be successful following the steps below:

Open Terminal and enter the following to get an overview:
```
diskutil list
```
The 3 TB disk is your external disk. In the next steps I assume the disk identifier of your external disk is disk1
Get the block size of the external disk:
```
diskutil info disk1 | grep "Device Block Size"
```
In the next steps I assume that the Device Block Size is 512 bytes. If you get another block size (i.e. 4096 bytes) leave a comment.

Get the partition table of the external disk:

sudo gpt -r show /dev/disk1

The result is similar to the output below (your sizes are different though):

       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34      262144      1  GPT part - E3C9E316-0B5C-4DB8-817D-F92DF00215AE
      262178        2014         
      264192  2244603904      2  GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
  2244868096  2048002015         
  4292870111          32         Sec GPT table
  4292870143           1         Sec GPT header

Unmount the external disk:
```
diskutil umountDisk /dev/disk1
```

Now add a third partition with

sudo gpt add -b 2244870110 -i 3 -s 1000000000 -t 48465300-0000-11AA-AA11-00306543ECAC disk1

I left some unallocated space (2014 blocks) between partition 2 and 3.

The resulting partition table looks like this then:

       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34      262144      1  GPT part - E3C9E316-0B5C-4DB8-817D-F92DF00215AE
      262178        2014         
      264192  2244603904      2  GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
  2244868096        2014         
  2244870110  1000000000      3  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  3244870110  1048000001         
  4292870111          32         Sec GPT table
  4292870143           1         Sec GPT header

You should choose a bigger size than 1000000000 blocks. The number of blocks has to be dividable through 8. The max size in my case would have been 2048000000 (1000000000 + 1048000001).

Now format the new partition with a file system and name the volume (in the example below Backup):
```
sudo newfs_hfs -J -v "Backup" /dev/disk1s3
```

Mount the volume and verify it:

diskutil mount /dev/disk1s3
diskutil verifyVolume /dev/disk1s3

Best Answer

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