Microsoft unveils new file system for Windows

Microsoft has unveiled its new file system, saying it will first arrive in Windows Server 8.

The Resilient File System (ReFS) builds on the existing NTFS, and is therefore largely compatible with it.

“We didn’t start from scratch, but reimagined it where it made sense and built on the right parts of NTFS where that made sense,” said Surendra Verma, a storage development manager, in a post on the Windows 8 blog.

Verma explained that ReFS will remain compatible with NTFS, keeping key features while “deprecating” less successful ones.

“ReFS inherits the features and semantics from NTFS including 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,” Verma said, while ditching “named streams, object IDs, short names, compression, file level encryption (EFS), user data transactions, sparse, hard-links, extended attributes, and quotas”.

ReFS will be accessible through the same file-access APIs, meaning any system that can access NTFS volumes will work with the new system.

Resiliency – if it wasn’t clear from the file system’s name – is a major focus, with all metadata verified using checksums and no longer written in place, to avoid “torn writes” if interrupted, such as by a power outage.

“In addition, we have added an option where the contents of a file are check-summed as well,” said Verma. “When this option, known as ‘integrity streams’, is enabled, ReFS always writes the changes to a location different from the original one. This allocated-on-write technique ensures that pre-existing data is not lost due to the new write.”

Storage spaces

ReFS is designed to work with Microsoft’s Storage Spaces, a new system which uses virtualisation to create storage pools to better manage data.

The two systems can be used separately, but together they add more features, notably allowing Storage Spaces to fix corrupted files uncovered by ReFS using mirrored copies, and “scrubbing” metadata to ensure it’s correct. “Scrubbing involves reading all the redundant copies and validating their correctness using the ReFS checksums,” said Verma. “If checksums mismatch, bad copies are fixed using good ones.”

ReFS will initially only be available with Windows Server 8, and then only for storage systems. It will eventually be rolled out to Windows 8 client and then as a boot volume, but Microsoft didn’t reveal a timeline.