Microsoft details Windows 8's ReFS file system

January 17, 2012 // 11:38 a.m.

Tags: #fat #file-system #microsoft #ntfs #refs #storage #windows-8

Microsoft has released the first firm details of ReFS, the new file system that will d├ębut with the launch of Windows 8 as a successor to the ageing New Technology File System (NTFS) standard.

In a highly detailed post to the Building Windows 8 MSDN blog, development manager Surendra Verma explains the ins and outs of the Resilient File System, or ReFS, which is designed to update the NTFS format that was first introduced with Windows NT back in 1993 as part of Windows NT 3.1.

Just as NTFS was designed to succeed FAT, ReFS succeeds NTFS. It takes a subset of the features that are widely adopted from NTFS, adding new abilities to protect against corruption and scale to extreme file system sizes.

'The key goals of ReFS,' Verma explains, 'are: Maintain a high degree of compatibility with a subset of NTFS features that are widely adopted while deprecating others that provide limited value at the cost of system complexity and footprint; Verify and auto-correct data; Optimize for extreme scale; Never take the file system offline; Provide a full end-to-end resiliency architecture when used in conjunction with the Storage Spaces feature, which was co-designed and built in conjunction with ReFS.'

The means of achieving these goals are various. ReFS will include checksums that provide integrity checking for metadata, along with integrity streams designed to provide - optional - protection for user data; a copy-on-write transaction model provides a more robust update mechanism; disk scrubbing is implemented to protect against latent disk errors; and the usual NTFS features including BitLocker encryption, access control lists and symbolic link support make the transition too.

The new file system isn't just about improving data resiliency, however, but about making the march to exa-scale computing. Where NTFS tops out at 16TB in its traditional implementation - though the specification allows for 16 exabytes (EB) in a single file system - Windows 8's implementation of ReFS will support file systems as large as 16EB (16,777,216TB) where possible. If that wasn't enough, the specification itself extends to 256 zettabytes, or 274,877,906,944TB.

While ReFS drops some features from the NTFS specification - including named streams, object IDs, short names, compression, file-level encryption via EFS, user data transactions, hard links, extended attributes and quotas - the standard is likely to prove popular among high-performance computing enthusiasts who need large-scale storage systems with commercial support.

Sadly, there are a few caveats. Unlike the move from FAT to NTFS on the desktop, there will be no way to convert an existing volume to ReFS without creating a new volume and copying the data manually. There's no support for booting from ReFS, with NTFS being retained as the file system of choice for boot drives; and you can't use ReFS on removable drives.

Unlike other large-scale file systems, there's also no deduplication facility or second-level caching facility. 'One side effect of its familiar, pluggable, file system architecture is that other deduplication products will be able to plug into ReFS the same way they do with NTFS,' Verma explains. 'ReFS does not explicitly implement a second-level cache, but customers can use third-party solutions for this'

While ReFS is currently a server-oriented file system, it provides a glimpse of the future: after all, NTFS started in Microsoft's server and workstation product line before making its way to the desktop with Windows 2000.

Are you pleased to see Microsoft looking towards the future, or disappointed that certain NTFS features - including the handy filesystem-level compression function - won't be around in future generations? Share your thoughts over in the forums.
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