Author Topic: Procedure to remove EFI partitions on GPT Mac OS X formatted disks  (Read 79472 times)

Offline skreeth

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Information of the issue:
This post provides info and solutions to resolve an issue Mac users will encounter when using disks formatted on Mac OS X which will be connected to Mede8er X3D series media players (as of this time version 3.0.4).  Basically what is witnessed when two disks are connected to the Mede8er X3D series media player, is that two empty Fat32 volumes (which should be invisible) will be mounted,  as well as the volumes containing the media on each disk. The issue here is that the Mede8er X3D series media players shouldn't mount the two Fat32 partitions. The result to the user is that the media will appear not on the volume as expected but on the other volume. For example, if USB disk 1 is named TV, and USB disk 2 is named Movies, the user will see the TV programmes on the Movies disk and the Movies on the TV Programmes disk. The Mede8er X3D is seemingly confused due to it mounting these blank Fat32 partitions.

Legacy Windows systems use the BIOS and must use a Master Boot Record (MBR) partition scheme with an NTFS format, these are not affected. Disks with a MBR partition scheme with an ExFAT format are also not affected. Windows will create disks of these configurations by default.

Background details:
By default, Disk Utility in Mac OS X will erase and format a disk as a Mac OS Extended Journaled (HFS+) format with a Globally Unique Identifier Partition Scheme A.K.A GUID or GPT. This is used for bootable or non-bootable disks (external storage) to be used with Mac OS X, or as external non bootable storage for other systems with HFS+ drivers. This GPT partition scheme creates a 209MB Fat32 partition for booting EFI capable machines, such as Intel based Mac's, UEFI based Windows 8+ 64 bit machines (non BIOS), and many Unix (BSD, Linux), UEFI systems. This Fat32 partition is hidden in Mac OS X Disk Utility and is not mounted. It can be shown when Disk Utilities Debug menu is enabled. It will be shown as the BSD identifier such as 'disk2s1' in Mac OS X 10.6.x. In Mac OS  X 10.9 (possibly even 10.7 & 10.8) , it is shown as 'EFI' and again, it isn't mounted.

For users of Mac OS X machines the EFI partition on these GPT disks will need to be removed so that the Mede8er X3D can behave properly so that disks are mounted as expected. This can be done in two different ways, one, using the graphical user interface, and two, for those who prefer a faster method, via the Terminal. I'll explain both methods and provide images to give a visual reference.

Note, this does not delete or erase any of your media data on the main partition, so no need to backup and copy back.

Graphical user interface method. This requires one terminal command to make the EFI Fat32 partitions visible.
===============================================================================
1. Launch Terminal.app, located at /Applications/Utilities/Terminal.app. We want Disk Utility show the debug menu which contains a menu option to show hidden disk partitions, so copy & paste this command into the Terminal and hit the enter key:

Code: [Select]
defaults write com.apple.DiskUtility DUDebugMenuEnabled 1
You can quit the Terminal now.

 2. Launch Disk Utility, located at /Applications/Utilities/Disk Utility
Click the Debug menu and select 'Show every partition'. You'll notice some greyed out partitions under the connected disks in the sidebar, it's greyed to signify it isn't mounted.



3. Click on the greyed out partition under the external disk we want to work on. It will show either the BSD disk identifier such as disk2s1 as in my images from Mac OS X 10.6.8 or 'EFI' if on 10.9, maybe even 10.7 & 10.8.

Click the 'Erase' Tab then click the 'Erase' button. You'll notice after this, the partition becomes mounted and the text is the normal shade of grey.



4. Now select the actual external disk in the sidebar which is on top of the partitions shown below it. You'll notice there is now a 'Partition' tab, click it. Under Volume Scheme, a visual reference of the partition is shown. Click the first small partition so it's highlighted, this is the one that was erased and mounted in previous steps. Then click the Remove button (minus icon).



5. Click the 'Remove' button from the drop down sheet. After this, the 'disk2s1' or 'EFI' partition will no longer be shown, in the sidebar, it's gone and only the main large volume containing your media files shall remain.



Final visual reference of Disk Utility after the removal of the EFI partition. Now eject the disk and plug into the Mede8er and the issue is resolved.



===============================================================================

Command line method, way faster.

Terminal commands to delete EFI Partition (in this case, it's disk2)

To show a list of the disks, type or copy & paste to Terminal and hit enter:
Code: [Select]
diskutil list
Identify disk with EFI partition (it's never disk0 this is internal), type or copy & paste to terminal and hit enter:
Code: [Select]
diskutil unmountDisk /dev/disk2
To remove the EFI partition, type or copy & paste to Terminal and hit enter:
Code: [Select]
sudo gpt remove -i 1 disk2
It asks for password, type in your admin password and hit enter. The terminal will show a confirmation of execution.

Sample image for reference:

« Last Edit: March 30, 2014, 03:26:32 am by skreeth »

Offline firstnoel

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Re: Procedure to remove EFI partitions on GPT Mac OS X formatted disks
« Reply #1 on: March 29, 2014, 08:41:18 pm »
This tip should be a sticky!

I was at loss on where that FAT32 partition comes from everytime I mount an HFS+ external drive. I thought it's a bug on the latest beta. Now we know!

The terminal command:

Code: [Select]
defaults write com.apple.DiskUtility DUDebugMenuEnabled
did not work for me in Lion. What worked was:

Code: [Select]
defaults write com.apple.DiskUtility DUDebugMenuEnabled -bool true
Otherwise, a very important tip. Kudos to OP!

Offline jer1956

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Re: Procedure to remove EFI partitions on GPT Mac OS X formatted disks
« Reply #2 on: March 29, 2014, 09:11:18 pm »
There is already a sticky tip on formatting HFS USB drives. That tip has now been modified to say if your version of ios gives you partition table options you must  use non bootable MBR.

So hopefully no one in the future will have to remove the problematic efi partition, but many people only look for help after they have got in a mess.


And someone has to be the first to get in the poo and dig themselves out.  So  thanks to the op for this tip.
« Last Edit: March 29, 2014, 09:18:42 pm by jer1956 »

Offline skreeth

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Re: Procedure to remove EFI partitions on GPT Mac OS X formatted disks
« Reply #3 on: March 30, 2014, 03:31:43 am »
This tip should be a sticky!

I was at loss on where that FAT32 partition comes from everytime I mount an HFS+ external drive. I thought it's a bug on the latest beta. Now we know!

The terminal command:

Code: [Select]
defaults write com.apple.DiskUtility DUDebugMenuEnabled
did not work for me in Lion. What worked was:

Code: [Select]
defaults write com.apple.DiskUtility DUDebugMenuEnabled -bool true
Otherwise, a very important tip. Kudos to OP!

Good pick up thanks. The number '1' was missing from my code.

There are two key variations that work to enable it.

Code: [Select]
defaults write com.apple.DiskUtility DUDebugMenuEnabled 1
Code: [Select]
defaults write com.apple.DiskUtility DUDebugMenuEnabled -bool true
To disable the debug menu:

Code: [Select]
defaults write com.apple.DiskUtility DUDebugMenuEnabled 0
Code: [Select]
defaults write com.apple.DiskUtility DUDebugMenuEnabled -bool false

Offline Maasbommel

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Re:
« Reply #4 on: March 30, 2014, 09:05:43 am »
Made it a sticky now.
Read the  Mede8er 400X/500X Beginners Guide
or Mede8er 500X2/400X2/450X2 Beginners Guide

Also check the Couto X3D Newbies Guide first.

Please don't PM me but post on the forum.

Offline zerojapan

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Re: Procedure to remove EFI partitions on GPT Mac OS X formatted disks
« Reply #5 on: April 07, 2014, 03:41:44 am »
This knowledge with me as well.

Offline wessongroup

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Re: Procedure to remove EFI partitions on GPT Mac OS X formatted disks
« Reply #6 on: August 15, 2015, 04:43:56 pm »
Was able to set up my MED1000X3D when using the PC HDD ... all functions worked

However, after reformatting the HDD, by connecting via the USB 3.0 and using the Disk Utility in my mac-min OS 10.10.4 to a mac HDD ... I can not select any features to once again set up the MED1000X3D

I can not move or select any function on the main menu

Followed the reformatting steps and have a disk which shows up on my Mac desktop, but, the mac disk appears to not work with the software

Have downloaded the most recent software, however, the USB Flash drive does not show up .. so I can not install the most recent version of the software for the MED1000X3D

Have tried to reformat the HDD, back to PC (FAT) but can not

Sorry I did not notice what versions of software was present when I first set up the unit

And now I'm basically locked out

Any help would be greatly appreciated

Offline kimnguyen

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Re: Procedure to remove EFI partitions on GPT Mac OS X formatted disks
« Reply #7 on: May 12, 2016, 09:37:28 am »



It does not solve the problem, the main partition did not gain back 300MB from EFI partition after EFI partition is erased. The main partition remains 931.19 Gb in total 931.51Gb of the disk, the same before the EFI partition was erased.
Seems that the system does not show EFI partition but still reserves 200-300MB for it.