A few months ago I decided to format an external HD that I wish to use with my Mac mini, but I can not use 100% of it.

In the formatting process, a partition called EFI appeared. When I open the Disk Utility app, the partition is not displayed, but it was displayed by the command line using diskutil.

Here is the Disk Utility:

enter image description here

From the command line: 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_HFS MAC HD                  881.0 GB   disk0s2
   3:         Microsoft Reserved                         16.8 MB    disk0s3
   4:       Microsoft Basic Data BOOTCAMP                118.9 GB   disk0s4

/dev/disk1 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *640.1 GB   disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:       Microsoft Basic Data HD Caio                 639.9 GB   disk1s2

How can I recover the space lost to disk1s1?

up vote 1 down vote accepted

EFI partition is a partition that stores boot files for operating systems, but since it is an external drive, it's not needed. When you erase your disk and create a new GUID Partitioning Table on it, macOS will automatically create an EFI partition. If you don't want that EFI partition, you have a few options:

  • You can erase your disk and create a new MBR instead of GPT. To do this, follow these steps:
    1. Open Terminal. You can use spotlight to find it
    2. Make sure your external disk is inserted. Type diskutil list and identify your disk (in the output you provided, it looks like it's disk1).
    3. Type diskutil eraseDisk JHFS+ MYDISK MBR diskX and replace diskX with the actual disk's identifier (for example, disk1)
    4. Your disk will be erased without an EFI partition now.
  • You can use diskpart.exe to partition the disk on Windows. Windows doesn't create an EFI partition.
  • I ran the command and the EFI partition simply disappeared instead of going back to the disk: /dev/disk1 (external, physical): #: TYPE NAME SIZE IDENTIFIER 0: FDisk_partition_scheme *640.1 GB disk1 1: Apple_HFS MYDISK 640.1 GB disk1s1 – Caio Kawasaki Jun 7 at 15:00
  • Should not partitions disk1s1 and disk1s2 merge? – Caio Kawasaki Jun 7 at 15:02
  • What do you mean? It looks like it's solved. – pixelomer Jun 7 at 15:02
  • 1
    They did. It was 639.9 GB and it merged with 200 MB so it's now 640.1 GB. – pixelomer Jun 7 at 15:03

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