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A 200MB "EFI System Partition" stuck on your USB drive and can't get it off?! READ THIS!


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#1
level70steve

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Okay, earlier, I was not so pleased with formatting a USB flash drive in an attempt to get an OSX installation going, I should've restored with a DVD image and that was when I screwed up. Now I can't use it in Windows XP/Vista/7/8 because not only it did not appear in Computer, but it also contains a senseless 200 MB partition.

#1 - On windows, open Command Prompt (cmd).

#2 - Type "diskpart", press Enter.

#3 - Type "list disk", press Enter - and it will tell you which drives are which, including USB flash drives. Since I only had a hard drive and one 16GB flash image, that gave me the idea as to which disk I will take into consideration. My hard disk was 0 and my USB drive was 1.

#4 - Type "select disk X" where "X" is the location of your troubled USB drive. Press Enter.

#5 - Type "clean" and then further down the line, you will see something weird a few lines down...

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\Administrator>diskpart

Microsoft DiskPart version 6.1.7601
Copyright (C) 1999-2008 Microsoft Corporation.
On computer: 7

DISKPART> list disk

  Disk ###  Status		 Size	 Free	 Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0	Online		   74 GB	  0 B
  Disk 1	Online		   14 GB	14 GB		*

DISKPART> select disk 1

Disk 1 is now the selected disk.

DISKPART> clean

DiskPart has encountered an error: Access is denied.
See the System Event Log for more information.

DISKPART>

And so, you get an "access denied" error and another window should pop up saying that the drive needs to be formatted.

#6 - Close both the CMD and the Format Disk windows, hold down "Windows Key + R" to bring up a short Run window, and enter "diskmgmt.msc". Press Enter to run this command and make sure you are logged into Windows as Administrator while using Enterprise, Business, or Ultimate packages. DO NOT UNDER ANY CIRCUMSTANCE USE HOME PREMIUM/BASIC!

#7 - In Disk Management, your flash drive should appear in a complete black bar and all "EFI System Partitions" should be wiped out after you just got through using DISKPART. Right-click anywhere within the black bar, click New Volume, and follow the instructions that gives you.

#8 - Lay back because it could take a while depending on how much storage your drive has.

Right now, I am still trying this and so far, this method has solved most of my formatting and flash drive usage problems. Will it do the same for your flash drives?! Good luck, everyone, and make sure you are observing the OSx86 revolution even if it kills you. :)

#2
Gringo Vermelho

Gringo Vermelho

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Yes...or you could just format it as FAT/MBR or DOS or whatever it says, with Apple Disk Utility.

Not sure if this really belongs in the Genius Bar, but thanks for sharing.

#3
level70steve

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For the version I was using, Disk Utility wouldn't let me reformat. And their rules appear that no matter how many partitions you create in a single drive, OSX will throw in a 200MB system partition drive to begin with. Similarly, Windows Vista/7/8 would throw in a system partition when formatting a hard disk as if it was the first time. This is an option for OSX users that can't reformat a Flash drive using Disk Utility.

#4
Gringo Vermelho

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No, you are wrong and this is why your post does not belong in the Genius bar (not sure where else to put it though):
Disk Utility will let you format anything but you may have to wipe whatever partition table is on it first.

Disk Utility only creates the invisible EFI partition on GUID aka GPT drives.

Look at these screenshots (sorry about the mess but you get the idea):
Attached File  Partition.png   75.42KB   102 downloads Attached File  Partition options.png   102.3KB   92 downloads

This is how you repartition and format a GUID drive with Disk Utility so that it can be used on Windows.

The other stuff you said is not entirely correct either:
The System Reserved partition only gets created during installation of Windows, and only when installing to a drive that is not already formatted.
It does not get created when formatting a drive from within Windows.





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