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I have a 3TB external drive that I recently partitioned and formatted to use to backup all my various computers -- two partitions, one NTFS and one HFS+. I did the initial setup using Disk Utility on an iMac, backed that up, then proceeded to back up 2 other Macs in the house.

Now, I'm trying to backup my Windows laptop, but the NTFS partition is not showing up. In my Disk Management console, it shows the disk with 4 partitions:

  • 200MB "GPT Protective Partition"
  • ~2TB "RAW" (this should be NTFS)
  • ~1TB "RAW" (This is actually HFS+)
  • 127MB Unallocated (Disk Utility didn't mention this...)

Of course, the NTFS partition shows up fine on all the Macs, provided they have NTFS-3G installed.

Here's the thing that might be throwing Windows off:

DISKPART> detail partition

Partition 2
Type  : 0B
Hidden: No
Active: Yes
Offset in Bytes: 210763776

Note the Type: 0B -- that's FAT32, though Disk Utility clearly lists it as NTFS.

Did NTFS-3G create the partition wrong? Is there a way to fix this without losing the data on the partition? I'd really like to make a backup of this Windows laptop pretty soon...

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The problem is the default partition scheme used by the Mac when you created the partitions. Mac OS X uses map scheme GPT (GUID Partition Table, EFI compatible), that's why there's a GPT partition .

Windows likes MBR (Master Boot Records) a lot - and Mac OS X can handle them as well. So you have to re-partition you external harddrive (you loose all the data, or buy iPartition - it can change partition schemes without loosing the data).

If you partition this drive in Mac OS X with Disk Utility be sure to click 'Options' in the 'Partition' window. There you can choose from 'GUID Partition Table', 'Apple Partition Map' and 'Master Boot Record'. And the last one is what you want.

Afterwards Windows (and Mac OS X too) will see the NTFS partition.

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  • A warning about this: although OS X can use MBR-format disks for most purposes, I believe Time Machine requires GPT, so if you're using that for backup on the Macs... It is actually possible to build a hybrid MBR+GPT table -- Apple's Boot Camp Assistant does this, but only if you start from a single-partition (HFS+ under GPT) setup.
    – Gordon Davisson
    Mar 15, 2012 at 16:17
  • Mmmh, I don't totally agree about the hybrid part. Every GPT is a hybrid, the GPT specs define that for backward compatibility (WP article).
    – boretom
    Mar 15, 2012 at 16:58
  • What (one part of) Bootcamp does is emulate a BIOS to Windows through EFI. This is necessary since Windows can't boot from GPT formated disk (yet). But your absolutely right regarding Time Machine. Even further, if you ever think about putting a Mac OS X on this external drive and you want to boot of it, it must use the GPT scheme (not 100% sure if that's still true).
    – boretom
    Mar 15, 2012 at 17:05
  • So, I have to correct myself and apologize to you Gordon. Hybrid GPT/MBR does exist. And booting a Mac OS X from MBR is possible too. The Mac OS X installer just doesn't support it but by cloning a existing partition one can get around that limit (from refit Myth and Facts).
    – boretom
    Mar 15, 2012 at 17:12

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