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I currently have a triple-boot on my MacBook (OS X 10.6.5, Windows 7, Ubuntu 10.10) which works very well. I'd like to now make an ExFAT storage partition that would be shared amongst the three OS's, with the importance on sharing between Windows and OS X. This is what it looks like right now:

$ diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk0
   1:                        EFI                         209.7 MB   disk0s1
   2:                  Apple_HFS MacOSX                  400.0 GB   disk0s2
   3:       Microsoft Basic Data BOOTCAMP                74.5 GB    disk0s3
   4:       Microsoft Basic Data                         25.3 GB    disk0s4

There are, it appears, 4 partitions on the drive already, since the EFI requires 200 MB in the beginning. I'm wondering if I were to add another partition whether that would mess up the GPT/MBR syncing that rEFIt does for me because there would be more than 4 primary partitions on the disk. I will likely use iPartition for this.

EDIT
To add to the complexity, for unrelated reasons I decided to switch from Ubuntu to Fedora on that last partition. During the install, my curiosity made me select the recommended two partition setup with /boot going on a 500 MB /dev/sda4 and / in an LVM on /dev/sda5. The drive now looks like this:

$ diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk0
   1:                        EFI                         209.7 MB   disk0s1
   2:                  Apple_HFS MacOSX                  400.0 GB   disk0s2
   3:       Microsoft Basic Data BOOTCAMP                74.5 GB    disk0s3
   4:                        EFI                         524.3 MB   disk0s4
   5:                  Linux LVM                         24.8 GB    disk0s5

When I re-synced rEFIt, it suggested an MBR table that only had the first 4 partitions on it. Will try to get that info to add to this next time I reboot.

EDIT
Turns out that that you can't have more than 4 primary partitions with the GPT/MBR sync. In retrospect, it all makes sense now. I decided to just go ahead and test this so I created a 25 GB partition on the end of the drive. Looks like this now:

/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk0
   1:                        EFI                         209.7 MB   disk0s1
   2:                  Apple_HFS MacOSX                  373.4 GB   disk0s2
   3:       Microsoft Basic Data BOOTCAMP                74.5 GB    disk0s3
   4:                        EFI                         524.3 MB   disk0s4
   5:                  Linux LVM                         24.8 GB    disk0s5
   6:       Microsoft Basic Data Transfer                26.6 GB    disk0s6

Used OS X to format the last partition as exFAT (volume name Transfer). Used rEFIt to sync the GPT and MBR tables. Only showed up to 4 (which answers this question), which doesn't show up in Windows (which was expected). Next, I downloaded an OS X binary of the gptsync.efi program that rEFIt uses from the InsanelyMac forums and ran the following command to select the GPT partitions I wanted in the MBR table (1, 2, 3, and 6):

sudo gptsync /dev/disk0 2+af 3-07 6-07

thinking that the MBR type is 07 as listed on the exFAT WikiPedia page. When I rebooted into Windows again, the partition showed up in diskmgmt.msc, but as a RAW format. Upon accessing it in Explorer, I get the option to format it. I decided to try using a different MBR code and ran the following command again in OS X:

sudo gptsync /dev/disk0 2+af 3-07 6-0c

which did not resolve the problem. A cursory search suggests that exFAT is only meant to be used on external volumes, and that Windows would not load an internal partition formatted as exFAT. So, two things: (1) I either still have the MBR code wrong or (2) it just won't be read by Windows.

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1 Answer 1

I did exactly this (Win7 64, Ubuntu 10 64bit, OS X 64 bit, and an ExFAT part). When I found out that Customs could search a laptop at will without a court order in violation of the Constitution, I chose to move the ExFAT to a 128GB ExpressCard SSD (100 GB ExFAT set up for user space, 8 for each OS swap file, and the leftover space as RAM for Win7 to use).

This way all three systems could use the ExFAT as user space, it wasn't physically on the computer (it's removable), and since I was using 2 drives (one for OS/Apps, the other for user space/swap space) I sped up my system (not a huge amount).

If I had to worry about anyone wanting to see what was on my computer, I simply removed the user/swap space. I have licenses for all the Apps and the OS's on my Apps/OS drive. There are no applications that are unlawful for me to own/use to the best of my knowledge. I use Launchbar to search my user space (because the database for it is kept on the user space not on the OS/App space like Spotlight). I just wanted to give you food for thought.

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I guess the main question is what did the MBR table look like in rEFIt in the setup used in your first sentence? –  fideli Nov 21 '10 at 15:57

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