Mount /home in Subfolder of Shared Partition – Ubuntu

I have a dual-boot Windows 8.1 and Ubuntu 14.04 machine. Currently, I have one ext4 partition that is being used as my '/home' mount point in Ubuntu, and one NTFS partition that I am using to redirect 'My Documents' and such on Windows. This way both OS's are automatically using these partitions for file storage "under the hood".

My question is this: is there a reasonable way to make both OS's automatically use the same partition for file storage, without butting heads, and continuing this "under the hood" behavior? Preferably I would like to have this partition contain one folder named 'Ubuntu' and another folder named 'Windows', with the 'Ubuntu' folder acting as the mount point for '/home' and the 'Windows' folder containing my redirected profile folders, like in my current setup.

Is this possible? I'm guessing the format would have to be exFAT or something of the sort. Would there be any downsides (such as speed loss) from using this approach? And if this is not very reasonable, is there another setup that would give similar effects?

EDIT:
Also, would it be reasonable to have a third folder on this partition for my Dropbox files (with each OS's dropbox program pointing to this same folder), so there is only one copy of my dropbox files on my disk?

Best Answer

Depends. Not for the whole of /home, if you need Unix-permissions for group. Given the current state of ext driver support in Windows, we would have to use FAT/NTFS for such a common partition, and they don't support Unix permissions. So applications like SSH and GnuPG will have trouble.

I do it in a bit more complex way: symlink ~/Documents and other such folders to their Windows equivalent on an NTFS partition. Permissions on these folders don't really matter much. Helps if you want to have Dropbox sync them. Of course, none of these are located on the partition containing Windows, but on a separate NTFS partition.

A better approach will be to change the locations of these folders. From the Arch Wiki, add these to ~/.config/user-dirs.dirs:

XDG_DESKTOP_DIR="$HOME/Desktop"
XDG_DOWNLOAD_DIR="$HOME/Downloads"
XDG_DOCUMENTS_DIR="$HOME/Documents"
XDG_MUSIC_DIR="$HOME/Music"
XDG_PICTURES_DIR="$HOME/Pictures"
XDG_VIDEOS_DIR="$HOME/Videos"

Replace $HOME/<blah> with your desired location.

On my laptop, all such folders are common to both Windows and Debian (and Arch), and I don't face problems, except with Dropbox. Dropbox occasionally replaces perfectly good files with their older versions and says it's a conflicted copy.

Both ways require that the partition be automounted. Especially in the case of the XDG variables, the partition needs to be mounted before they're read, or they will reset to $HOME. See How to automount NTFS partitions? for guides on automounting NTFS partitions. The most preferable way to do so is editing /etc/fstab - any other option will mount after the partitions listed in that file are mounted.