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I've got a USB hard drive that I've been using with my Mac for backups, formatted as one large HFS+ partition. I added a second NTFS partition for similar use with Windows, as follows:

  1. Resize HFS+ partition using Mac OS X Disk Utility

  2. Reboot into Windows 7 using Bootcamp

  3. Add NTFS volume in the free space using Windows 7 Disk Manager

Now that I've done this, I can see both volumes in Bootcamp Windows, and they seem to be fine.

When I boot into Mac OS X, though, only the NTFS volume appears.

Looking at the disk in Disk Utility, the reason is clear: Mac OS X can't actually see any HFS+ partition there. Its space is shown as "disk4s2", and when I click on it in Disk Utility it's supposedly in "MS-DOS (FAT)" format. diskutil on the command line has this to say:

~% diskutil list /dev/disk4
/dev/disk4
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk4
   1:                        EFI                         209.7 MB   disk4s1
   2:       Microsoft Basic Data                         700.0 GB   disk4s2
   3:       Microsoft Basic Data BACKUPS                 300.0 GB   disk4s3

Nevertheless, when I reboot into Windows 7, the HFS+ partition pops up again, correct volume label and everything. So clearly the data is still there, and in some kind of usable format.

It's not the end of the world if I have to reformat, but I'd rather keep my full Time Machine history if possible. So is there something I can do to fix this non-destructively, and should I have done something differently when I was adding the second partition?

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1 Answer 1

up vote 2 down vote accepted

I tried various other search terms and found that this question is actually a duplicate of this one: OS X 10.6 Snow Leopard no longer mounting an external USB drive.

Here's what I did to fix:

  1. Download and install GPT fdisk
  2. Run gdisk and select problem drive:

    ~% sudo gdisk
    GPT fdisk (gdisk) version 0.8.1
    
    Type device filename, or press <Enter> to exit: /dev/disk3
    Partition table scan:
      MBR: protective
      BSD: not present
      APM: not present
      GPT: present
    
    Found valid GPT with protective MBR; using GPT.
    
  3. Look at the partitions using the p command:

    Command (? for help): p
    Disk /dev/disk3: 1953525168 sectors, 931.5 GiB
    Logical sector size: 512 bytes
    Disk identifier (GUID): ABFA9105-73F4-4627-9890-9DECC55E86AC
    Partition table holds up to 128 entries
    First usable sector is 34, last usable sector is 1953525134
    Partitions will be aligned on 8-sector boundaries
    Total free space is 3389 sectors (1.7 MiB)
    
    Number  Start (sector)    End (sector)  Size       Code  Name
       1              40          409639   200.0 MiB   EF00  EFI System Partition
       2          409640      1367597143   651.9 GiB   0700  Time Machine Backups
       3      1367599104      1953523711   279.4 GiB   0700  Basic data partition
    

    In this case, it's partition 2 that's causing the problem. And the problem is that its type code is 0700, which means something other than HFS.

  4. Use the t command to set the partition type to af00 - Apple HFS/HFS+.

    Command (? for help): t
    Partition number (1-3): 2
    Current type is 'Microsoft basic data'
    Hex code or GUID (L to show codes, Enter = af00): 
    Changed type of partition to 'Apple HFS/HFS+'
    
  5. Use the w command to write the stuff back to disk and quit.

    Command (? for help): w
    
    Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
    PARTITIONS!!
    
    Do you want to proceed? (Y/N): y
    OK; writing new GUID partition table (GPT).
    Warning: The kernel may continue to use old or deleted partitions.
    You should reboot or remove the drive.
    The operation has completed successfully.
    

The HFS+ partition, and all of its contents, then became visible again to OS X.

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