Microsoft's ReFS Filesystem for Windows 8 Server Explained

While Windows 8 client machines will continue to use the NTFS filesystem, Microsoft's Surendra Verma has given us some details on Windows 8 Server's new "Resilient File System," or ReFS. ReFS is meant to maintain compatibility with the most frequently-used features of NTFS, including Bitlocker encryption compatibility, Access Control Lists (ACLs) to control permissions, change notifications, symbolic links, and others, while shedding legacy features and picking up new ones to make it more useful and versatile on today's drives.

ReFS's server-oriented features work best in conjunction with Storage Spaces, which we discussed last week - if you don't remember, Storage Spaces is a feature available for both NTFS and ReFS volumes that can provide redundancy and pooled storage for numerous internal and external drives of different sizes and interfaces. Where Storage Spaces provide protection from disk failure, one of ReFS's primary goals is to combat data corruption, including situations where a write operation to the disk is interrupted, where data is written to the wrong area of a disk due to a software or firmware bug, and "bit rot," where data on infrequently accessed sections of a disk degrades over time.

ReFS  uses a feature called "integrity streams" to combat file corruption - when enabled, whenever a file is changed, the modified copy is written to a different area of the disk than that of the original file. This way, even if the write operation is interrupted and the modified file is lost, the original file is still intact. When combined with Storage Spaces, which can store a copy of all files in a storage array on more than one physical disk, ReFS gives Windows a way to automatically find and open an uncorrupted version of a file In the event that a file on one of the physical disks becmes corrupted.

To combat bit rot, ReFS (again, when combined with Storage Spaces) uses its "scrubbing" feature to read all copies of a file in the array and compare their metadata with one another. If a corrupted file is found anywhere in the array, it is replaced by a good copy. This is especially useful in the case of infrequently accessed data, which could become corrupt in between reads without anyone noticing.

Microsoft expects ReFS to be production-ready when Windows 8 Server is released to the public, but the filesystem will still be rolled out conservatively: it will first be available for Windows 8 Server, then for client operating systems, and then finally as an option for boot volumes. Whether ReFS will come to clients in a Windows 8 service pack or as part of another OS was not discussed, but Microsoft clearly intends it as a full-on replacement for NTFS in the long run - while it has been updated a few times over the years, the NTFS specification has been around since Windows NT 3.1 was introduced in 1993, and its last potential successor (WinFS) was among the many features cut from Windows Vista during its notoriously rocky five-year development cycle.

Source: Building Windows 8 Blog