completelydifferent
Totally useful graph explaining the difference between NTFS and ReFS

A widely rumored file system makeover called ReFS, for Resilient File System, is indeed coming to Windows 8. But it won't appear in the client OS that will be purchased by hundreds of millions of people each year. Instead, it will be relegated to the Windows Server 8 OS for servers only.

This feature is completely irrelevant to Window 8 and its users.

Microsoft admitted the long-rumored existence of ReFS in a curiously timed, Sunday Monday (federal holiday) night post to its Building Windows 8 Blog. Which is further curious, since Microsoft has a separate blog, the Microsoft Server and Cloud Platform Blog, which would have been more appropriate.

In keeping with the most recent B8 blog posts, a Q&A appears at the end. This seems aimed at heading off the most common questions that enthusiasts will have and thus framing the debate.

OK, but what did Microsoft say about this new file system?

First of all, it's not new. ReFS is an evolution of the durable and well-understood NTFS file system. It retains a "high degree of compatibility with a subset of NTFS features," which translates in simple English to "only some compatibility with NTFS". It's highly scalable, which explains why it's a server-only file system, and features "end-to-end resiliency" when used in combination with the previously-revealed Storage Spaces feature.

From a developer perspective, ReFS is identical/very similar to NTFS. That is, its uses the exact same file access APIs, though I'd imagine some new features require new APIs.

From a user perspective, ReFS can access the same "features and semantics" as NTFS, which Microsoft describes as BitLocker encryption, access-control lists for security, USN journal, change notifications, symbolic links, junction points, mount points, reparse points, volume snapshots, file IDs, and oplocks.

No longer supported, however, are NTFS features like named streams, object IDs, short names, compression, file level encryption (EFS), user data transactions, sparse, hard-links, extended attributes, and quotas. There's no deduplication feature either.

"ReFS forms the foundation of storage on Windows for the next decade or more," Microsoft's Surendra Verma writes in the post. "We believe this significantly advances our state of the art for storage. Together, Storage Spaces and ReFS have been architected with headroom to innovate further, and we expect that we will see ReFS as the next massively deployed file system."

Put simply, ReFS is exactly what it sounds like: An evolved and improved version of NTFS that is more scalable and more resilient and, in the current guise, relegated to Server only. You cannot boot a PC with this file system and it cannot be used on removable storage. It doesn't take a rocket scientist to predict those features are coming in Windows 9.

Why the name change? Because as part of Microsoft's "reimagining of Windows," it must thus also "introduce a newly engineered file system." I'm surprised it's not just called NTFS vNext, frankly. And I'm surprised that Microsoft's capacity limits table didn't also include NTFS data for comparison.

Be sure to read the original blog post, which is as dense as it sounds. It's also completely irrelevant to the Windows 8 client.