Flashdrive stuck at 200 MB

Question

I’m a Mac OS 10.11.

I've tried to build a bootable images USB flashdrive on 2 of my flash drives, now I want use them as a storage again. I want to format them.

But they seems to stuck in 200 MB EFI mode partition or something like that, and no matter what, I can’t seem to format it back to it original size (32 GB).

I’ve tried MS-DOS, and ExFAT. Both give me same result. :(

How do I force format my flash drive back to its original size on a Mac OS X 10.11 ?

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Result of diskutil in Terminal

/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage Macintosh HD            499.4 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           +499.1 GB   disk1
                                 Logical Volume on disk0s2
                                 5866A45F-D1A4-43E9-9719-881FBA5840F6
                                 Unencrypted
/dev/disk2 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     Apple_partition_scheme                        +205.1 MB   disk2
   1:        Apple_partition_map                         32.3 KB    disk2s1
   2:                  Apple_HFS Google Chrome           205.1 MB   disk2s2
/dev/disk3 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *32.0 GB    disk3
   1:                        EFI EFI                     209.7 MB   disk3s1
   2:       Microsoft Basic Data USB 3.0                 31.8 GB    disk3s2

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Updated

I've format it to ExFAT.

Mac OS X

When I plug that drive into a Mac, I got it to display fine with full capacity.

Windows

But when I plug it into my Windows PC, I kept seeing this EFI partition - not the other one.

What is the cause of that ? How do I prevent it ?

I'm running out of ideas now. :('''

Answer 1

Your flash drive is partitioned using the GUID Partition Table scheme. You need to partition the flash drive using a Master Boot Record scheme. Also you should choose to only have a single partition.

Answer 2

Your problem is that you have two partitions and Windows is not able to read one of them by its extension. To solve it follow this:

1. Open Disk Utils. (It is in your Utilities folder inside of Applications).

2. Select your USB in the left menu (Select the device not the partition)

3. Once you have selected the device, partition option in the top menu will be enabled. If you click on it, you should see something like this:

4. You should see the chart divided in two (EFI and Microsoft Basic Data partitions of your USB). In order to remove one of them just click in "-" button, and you should see how all the usb has now only one partition.

5. Then rename your partition with your favorite name, and select format (I recommend you Exfat because it can be read both Windows and Mac and is much better that Fat32 since it has no 4GB limit for files)

6. Finally just click Apply and you should have your USB formatted.

Remember that if you want, you can create more partitions in your USB but you must choose the correct format for each one, in order to be able to read it on multiple SO.

I hope it helps you.

Answer 3

You can try force format using terminal

1. Enter this in the terminal "diskutil list"
2. Then a list of devices will be shown.
3. "diskutil eraseDisk JHFS+ diskname diskidentifier" replace disk name with device to formatted. In the command above, change “JHFS+” to “HFS+” if you want a volume that is not journalled. Change “diskname” to the new name you want for the disk, and replace “diskidentifier” to the Disk Identifier obtained from Disk Utility. If you want to reformat, replace eraseDisk with reformat and delete the “JHFS+” and “diskname” parts of the command.

You can try the above steps. Hope this will help.