OneDrive users around the world have been upset to discover that with its latest update, Microsoft's cloud file syncing and storage system no longer works with anything other than disks formatted with the NTFS file system. Both older file systems, such as FAT32 and exFAT, and newer ones, such as ReFS, will now provoke an error message when OneDrive starts up.

To continue to use the software, files will have to be stored on an NTFS volume. While FAT disks can be converted, ReFS volumes must be reformatted and wiped. This has left various OneDrive users unhappy. While NTFS is the default file system in Windows, people using SD cards to extend the storage on small laptops and tablets will typically use exFAT. Similarly, people using Storage Spaces to manage large, redundant storage volumes will often use ReFS. The new policy doesn't change anything for most Windows users, but those at the margins will feel hard done by.

In a rather odd statement made to OnMSFT, Microsoft said that it "discovered a warning message that should have existed was missing when a user attempted to store their OneDrive folder on a non-NTFS filesystem—which was immediately remedied." The company's position, apparently, is that OneDrive should always have warned about these usage scenarios and that it's only a bug or an oversight that allowed non-NTFS volumes to work.

Our suspicion is that the change is driven by the forthcoming release of the Windows 10 Fall Creators Update (FCU). The FCU includes a huge revamp of OneDrive's functionality to make the use of local and remotely stored files virtually seamless. This new system relies on features that NTFS supports but FAT and exFAT do not. Getting people to migrate their data now will help streamline the release of the FCU, currently expected in September.

What's not so clear is why Microsoft's brand-new ReFS file system is also excluded. ReFS does not support every NTFS feature, and it's possible that OneDrive uses one of the features missing from ReFS—though the main feature that OneDrive leverages, reparse points, is available on ReFS. If this is in fact the case, it just raises another question: why didn't Microsoft ensure that the new OneDrive client worked on its newest file system, or conversely, why hasn't Microsoft updated its newest file system to support the relevant missing features?