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I just bought a Mac Mini. Before I even booted it up I installed a 256 GB SSD along side the stock 1 GB hard drive, and reinstalled Mac OS and Windows 8 on the new drive using bootcamp. Everything is working fine, but I'd like to reformat the stock drive as one big NTFS partition so I can use it as shared storage between the OSes.

When I view the drives in Apple's Disk Utility, it shows the following partitions:

256 GB SSD:

  • SSD - Mac OS Extended (Journaled) (A silly name for my new Mac OS partition)
  • Bootcamp - NTFS (A silly name for my Windows 8 partition)

1TB Apple HDD

  • Macintosh HD - Mac OS Extended (Journaled) (The original Mac OS install from the factory)

When I view the drives in Windows Disk Manager, it shows the following partitions:

Disk 0 (1TB hard drive)

  • 200 MB Healthy (EFI System Partition)
  • 930 GB HFS Healthy (Primary Partition)
  • 620 MB Healthy (Primary Partition)

Disk 1 (256 GB SSD)

  • 200 MB Healthy (GPT Protective Partition)
  • (E:) 118 GB HFS Healthy (Primary Partition)
  • 620 MB Healthy (Primary Partition)
  • BOOTCAMP (C:) 119 GB NTFS Healthy (System, Boot, Page File, Active, Crash Dump, Primary Parition)

When I try to erase the 1 TB drive in Apple's Disk Utility, it gives me an error saying "Disk Erase failed with the error: Couldn't unmount disk". Is my old drive still holding something important, like a master boot record or whatever the modern equivalent to that is? Should I use Windows to try to erase the 1 TB drive? I'm pretty confident I'm booting into the copy of Mac OS on the new SSD, because the bootcamp startup screen shows the OS partition on the old drive as well, and I'm selecting the new one. The EFI partition on the old drive seems suspicious to me, is bootcamp using this or something?

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migrated from Oct 15 '13 at 4:30

This question came from our site for system and network administrators.

Disconnect the second drive. Then boot up. If all is good. Just reformat the second drive and delete the partitions.

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"We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed." – gparyani Feb 1 '14 at 21:47
The reason I haven't disconnected the drive is that it is very difficult to get to the hard drive to disconnect it in the Mac Mini. It is at least an hour process to get the drive disconnected and then I have to put the thing back together. It is really not designed for the end-user to be able to do anything more than add more RAM. I was unable to figure out how to do the Mac equivalent of disabling the drive in the BIOS either. – KOTJMF Feb 18 '14 at 18:02

I wasn't able to solve this problem without reformatting my disks. What I ended up doing was downloading a freeware utility that I copied to a bootable USB jump drive that let me do a bit-wise erase on my drives. I then started from scratch, partitioned my SSD and made sure my OSes were installed only on that drive. Not the easiest solution, as erasing the drives took multiple hours for each drive, but I got the results I was looking for in the end.

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