Windows Server 8 to Get a New File System: ReFS

Microsoft will be introducing a new file system with Windows 8 Server, called ReFS, which is built on top of the existing NTFS, but will deliver new features for scale and prevent data corruption.

ReFS, short for Resilient File System, will initially debut with Windows 8 Server, but is expected to make its way through to Windows 8 client system to support the full feature set of Storage Spaces, which will allow users to create storage pools from multiple physical and virtual storage devices.

According to Microsoft, ReFS will be an always-online file system "for the next decade or more" that is architected for "extreme scale" with large volume, file and directory sizes, as well as data verification and auto-correction via checksums while maintaining compatibility with a "wide subset of widely adopted" NTFS features.

ReFS will support a maximum size of 4 PB per storage pool path and file lengths of up to 32,000 (unicode) characters, up to 2^64 (18,446,744,100,000,000,000 or about 18 quintillion) directories in a storage volume, and up to 2^64 files in a single directory. ReFS also supports, in theory, to a maximum volume size of 2^78 bytes, as Windows stack addressing is limited to 2^64 bytes, which translates to 16,384 PB. The file size limit is 2^64-1 bytes.

REFS's most critical feature, however, may be its ability to answer data corruption on-the-fly, as all ReFS metadata is check-summed across multiple volumes (in storage spaces environments), which enables the technology to detect disk corruptions. If the user chooses to activate file checksums (integrity streams) as well, ReFS will always give preference to the original file over the newer file. "This allocate-on-write technique ensures that pre-existing data is not lost due to the new write," wrote Surendra Verma, a development manager on Microsoft's Storage and File System team. "The checksum update is done atomically with the data write, so that if power is lost during the write, we always have a consistently verifiable version of the file available whereby corruptions can be detected authoritatively."

Just like NTFS, Microsoft will be testing and deploying ReFS in server environments initially. However, its feature may have true advantages in combined server-client environment, especially if we include cloud-computing services and storage pools. Expect ReFS to become available on your desktop and notebook PC in the foreseeable future as Verma noted that ReFS will be "the next massively deployed file system."