iMac dual-booting Mavericks and Windows 8.1, trying to extend 8.1 partition

Question

So once upon a time, I had 2 partitions: 800GB for OS X, and 200 for Windows 8. With the 8.1 update, I would like to start using Windows more, and I proceeded to free up 300GB of OS X space, which is now listed on the drive as "Unallocated space".

Now I would like to merge this with my NTFS Bootcamp partition. This has proven extraordinarily difficult because in the Disk Management program in Windows, the unallocated space is to the left of the 200GB Windows partition, and the merge/extend options are all grayed out. My current understanding is that if the unallocated space is to the RIGHT of the Windows partition, everything will work just fine.

I have tried the built in Disk Management, AOMEI, and EaseUs, all with similar failings.

It is worth noting that I tried to format the unallocated space to NTFS with each program, only to be constantly informed that there was "not enough space" to make the change. Even by reducing the target drive size by a full 10GB, it gave the same message.

What do I do?

Answer 1

First, and most importantly:

DO NOT USE WINDOWS UTILITIES TO MODIFY YOUR HARD DISK!!!!!!!!!!!!!!!!!!!!!!

In Boot Camp installations, the hard disk uses a hybrid MBR, which is an ugly and dangerous hack that involves taking the standard Mac GUID Partition Table (GPT) partitions and creating an MBR data structure that duplicates up to three of them. This is done to make Windows happy, and the trouble is that the standard Windows disk partitioning tools will act only on the MBR data structures -- but the real disk partitions are GPT, so any modification of the MBR data structures that doesn't take the GPT partitions into account will create inconsistencies between the two partition tables. The result can be lost data -- often lost to the point where it's very difficult to restore.

If the OS X disk utilities won't modify your partitions in the way you want, you'll have to use something else. I'm not sure what third-party OS X tools are available, but the Linux GParted tool may well do what you want. If you don't normally use Linux, you can still use a Linux live CD, such as an Ubuntu live CD or System Rescue CD. There are some caveats, though:

• As with any disk partitioning operations, you should be sure to back up before you do anything. Moving or resizing partitions usually goes smoothly, but when it doesn't, the results can be bad, up to and including total loss of all data on the hard disk. Prepare for this and you won't have any regrets.
• GParted and some other tools will wipe your hybrid MBR. You'll therefore need to restore it. You can do this most flexibly with gdisk, but the gptsync utility (which comes with rEFIt, and an updated version with rEFInd), is easier to use.
• Adjusting the start point of a Windows boot partition is likely to result in an inability to boot Windows. You may need to restore the Windows boot loader using a Windows emergency disc. Have such a disc ready and read up on the procedure to be ready. Do this only after restoring your hybrid MBR.