Windows 10 vs Windows 7 GPT filesystem incompatibility?

Question

Good evening, I've got a dual boot system with Windows 10 and Windows 7 installed on one HD, and my second HD is an empty one for storing multimedia and games. Both disks are formatted as GPT.

I've noticed a very strange issue that whenever I write files to that second drive while running under Windows 10, I can read those files afterwards in Windows 7 without a problem, but if I write files to the second drive using Windows 7, and try to access them using Windows 10, I don't see the folders. At the very least I see the folder, but Windows 10 tells me it's inaccessbile or corrupted, even after granting myself access permissions (popup window).

But when I formatted the second HD as MBR, this problem dissapeared; both systems can now write and cross-read each others' files just fine, and also that annoying dialog stating I need to grant myself permission to read the files written by the other OS doesn't seem to pop-up anymore.

What is going on here? Anyone got any idea? WIndows 7 runs fine on the primary GPT disk, why would there be conflicts like this when sharing the second GPT drive?

Thanks a lot.

Answer 1

First, the Master Boot Record (MBR) and the GUID Partition Table (GPT) are partition table types; they're ways to encode the start and end points of partitions, as well as other partition metadata. They are not filesystems. The term "format" is generally applied either to extremely low-level data structures (a usage that's rare these days) or to mean the creation of a filesystem -- that is, to lower- or higher-level constructs than the partition table.

Chances are the problems you encountered were related to the New Technology File System (NTFS), which is the filesystem used natively by modern versions of Windows. I don't know of any differences between the way Windows 7 and Windows 10 create or manage NTFS; however, there is one difference that could explain your problem: Windows 8 and later implement a feature called Fast Startup, in which a shutdown operation becomes a suspend-to-disk operation. This results in filesystem data structures being left in an inconsistent state. If you then boot another OS (Linux, OS X, or another version of Windows), it will see the disk as if the previous OS had crashed and try to repair it. When you reboot to Windows 10, it will see a "repaired" disk and won't know what to do with the data it's cached but not yet written to disk. The end result can be lost files, as you describe, and potentially much more serious problems.

The solution is to disable Fast Startup. Doing so is described here, among other places. You may also need to disable the Windows 10 Hibernate feature, which is related; see here for more information. Note that Fast Startup and Hibernate are Windows features. Many EFIs have a feature called "fast start" or something similar. This feature is completely unrelated to the Windows feature and should not cause this type of problem.

As to why the problem disappeared when you used MBR rather than GPT, it could be you just got lucky on the MBR use; or it could be that Windows doesn't use Fast Startup on MBR disks. (I don't know if there are GPT-vs-MBR differences on how Windows uses this feature.)