Not all partitions are shown on an HFS disk.

If there are more than 4 partitions on an HFS disk, some of them don’t appear in Windows.

What causes this situation.

Macintosh Disk Utility creates a Hybrid GPT disk whenever user wants to make more than 1 partition on a disk and one or more of these partitions is non-HFS.

Hybrid GPT also contains MBR table. But as MBR has a limitation of 4 lines of code (4 partitions), GPT part has all and MBR part has only 4 first partitions. Furthermore, if user adds any non-HFS partitions to a disk, Disk Utility will automatically change partition table type to Hybrid GPT regardless of partition table that was there before.

On the other side, Windows reads MBR first. And as it sees a valid MBR it works with it instead of trying to read GPT. Although it can see GPT and show all the partitions in Disk Management, it can only mount first 4.

How to fix it.

The easiest way is to format your disk from scratch using Terminal to create a standard GPT table.

But if you have data on that drive you you don’t want to lose and cannot backup, there is a way to use Terminal to change your MBR into Protective MBR (which is defensive measure against older systems that don’t recognize GPT).

Be warned that converting your MBR includes Terminal commands that might ruin it if not used correctly.

1. Connect your disk. In our example it will have address /dev/disk4. You should first take a look at your disk address.
2. Unmount all partitions using command:
diskutil umountDisk /dev/disk4
3. Run this command to start editing MBR:
sudo fdisk -e /dev/disk4
After this command your input line should look like this: fdisk: 1> 4. To ensure you see your MBR properly, run this command:
print
5. If you see the proper MBR, you can proceed to editing. Run this commands:
edit 2
Partition id (‘0’ to disable) [0 – FF]: [AF] (? for help) 0 6. Repeat editing with partitions 3 and 4.
7. Edit partition 1 this way:
edit 1
EE
Do you wish to edit in CHS mode? [n] (Press Enter here) Partition offset [0 – 195312500]: [63] 1 8. Check if you didn’t make any mistakes. If everything is correct, execute changes to MBR with this command:
write
9. Exit editing with this command:
exit
10. To ensure you have done everything correctly, run this command:
sudo fdisk /dev/disk4
It should say that you have only 1 partition with “Unknown ID” which takes the whole disk.

This is a Terminal output example: link

General, HFS+ for Windows, NTFS for Mac OS X
Tags: bootcamp, error, howto, issue, mac, windows

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