I have two OS here, Ubuntu and OS X in my Macbook Pro. I want to centralize my data and separate OS filesystem. So, when I need to re-format or upgrade my OS (Ubuntu/OSX), my data stil save can easily accessed from both. Ubuntu and OS X should be able to accessing this partition. So, it is simple tricks.
1. Disk Utility
Go to your OS X and open Disk Utility. Create new partition which this will be your data partition.
Format it using HFS without Journaled. Now, every your works on OS X, you should put all data in here.
2. Go to Ubuntu
We will use this HFS non-journaled which contain our data as user home folder.
Open your nautilus and click on this new partition to mount.
df -hT to check where this partition located, eg : "/dev/sda3".
You should copy all your current "HOME" files into this new partition.
Don't forget to show all hidden files.
In case it can't be written, you can do "sudo chmod 777
Edit "/etc/fstab" and load this partition into your /home/
/dev/sda3 /home/ubuntu hfsplus defaults,rw 0 0
Make sure you already have "hfsplus", "hfsutils" and "hfsprogs" installed in your Ubuntu.
Then you can reboot and next boot your Ubuntu will use HFS partition as home folder :)