OS X Partition split and duplicated when creating Boot Camp partition

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OS X Partition split and duplicated when creating Boot Camp partition

Hi,

I have installed a larger internal HD 3TB into my iMac Late 2009 21.5 inch. All went well until I used Boot Camp to set up a Windows partition. My intention to have an OS X partition of 2.8TB and a Boot Camp partition of 200 GB. I am running the latest version of Yosemite.

Once the Boot Camp partition completed, and Windows 7 installed successfully, I have rebooted in OS X to find that the HD is now showing as a Partition of 200GB for Boot Camp, a partition of 2TB for Macintosh HD (with all my applications and data etc), and a second Macintosh HD partition of 800GB, also containing all my applications and data etc which appears to have been duplicated. Prior to completing the Boot Camp process, the internal HD was showing correctly as a single partition of 3TB.

I have completed this process twice, with the same result. After the first occasion, I reformatted the new internal HD and started completely from blank again (as I was unable to erase or change the duplicated partition in Disk Utility).

I used Migration Assistant to transfer my files, data etc from the old Internal HD which is now an external HD.

Any thoughts on what I am doing incorrectly?

iMac, OS X Mavericks (10.9.2)

Posted on Apr 26, 2015 6:12 AM

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Answer 1

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Loner T

Level 9

59,471 points

Apr 26, 2015 6:28 PM in response to cjtm

This is expected behavior. On your Mac, the 3TB disk is partitioned to allow Windows to function properly in BIOS mode. BIOS mode (and CSM-BIOS, to be precise) has a limitation of a 2TB disk. on a larger disk (including 3TB Fusion drives), the disk is partitioned in such a manner that the Windows adheres to the 2TB limit.

You can can see the exact partitioning, if you are so inclined, using the following Terminal commands.

diskutil list

diskutil cs list

sudo gpt -vv -r show /dev/disk0

sudo fdisk /dev/disk0

The "sudo" commands will prompt for your password, and it will not be echoed back. You may also see a warning about improper use of "sudo" and potential data loss due to "abuse" of the command.

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Answer 2

cjtm Author

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Apr 26, 2015 6:34 PM in response to Loner T

Thank you for your reply, that explains what I was puzzled about. Some questions however:

1. Will the second 800GB partition be usable?

2. I have used Camptune X in the past to adjust the Boot Camp partition size. When trying to use it now Camptune indicates I have "no Boot Camp configuration on the system". It is definitely there and usable...

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Answer 3

Loner T

Level 9

59,471 points

Apr 26, 2015 9:57 PM in response to cjtm

After BC partitions the disk and you have Windows installed, you can post the output the commands, and it can be verified. Compton can only see the MBR and may have issues if the partition for Windows starts before the 2TB boundary, but spans it. I would not recommend CampTune X, till you ask their Tech Support folks if this configuration is fully supported.

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