Microsoft releases Windows Server 8 file system details

Microsoft has released details of the filesystem developed for Windows 8. ReFS stands for Resilient File System and the new file system will only be used for the server version of Windows 8 for now.

The ReFS gets its name from its resistance to hardware and software errors; for example, in the event of a power failure, data on a server with ReFS should not be lost. Despite the new name, ReFS is still partly based on the well-known NTFS, which is used in current Windows products, for reasons of compatibility. ReFS was not going to replace ntfs in consumer versions of Windows; only Windows 8 Server would use the new file system.

In a blog post one of the developers of ReFS explains the main features and design criteria of the file system. In addition to backwards compatibility with NTFS, the file system must be suitable for very large storage volumes and corrupted data must be repaired automatically, while the file system remains available at all times. Volumes could also be distributed across different disks and systems to optimize availability and distribute load.

The data is written by a newly developed storage engine in so-called B+ trees. Not only the data itself, but also metadata such as directory structures are stored in tables in these B+ trees. Changes to files are always written to a different location than the original, which should prevent data corruption in the event of a write error.

The updated file system structure supports files that can be up to ten trillion bytes in size, while a volume can be as large as one stepcilillion, or 10^78 bytes. A volume can contain ten trillion directories, each of which can contain the same number of files. A storage pool has a maximum size of 4PB, but there is no limit to the number of storage pools. By the way, Windows Server 8 cannot boot from a ReFS disk; it is intended purely as a storage medium.