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Microsoft ReFS tuned for Hyper-V, but be aware of hazards

Microsoft positions its Resilient File System to replace the venerable NTFS, and it does increase resiliency and storage, but there are caveats that might limit its adoption.

While Microsoft's New Technology File System has long served as the cornerstone of endpoint and server-side data...

storage, the venerable technology is showing its age in the face of evolving compute and data storage demands.

In Windows Server 2012 and later releases, Microsoft added the Resilient File System (ReFS) to overcome some of the limitations with NTFS. Microsoft ReFS can increase resiliency and performance for storage volumes, but there are some drawbacks.

Microsoft ReFS isn't fully compatible with NTFS -- this can leave some enterprise utilities, services and workloads without proper support at the storage volume level. Measure the benefits and drawbacks to Microsoft ReFS before deploying this file system on storage systems.


Microsoft created ReFS to address the performance and integrity issues that have plagued the NTFS.

Microsoft created ReFS to address the performance and integrity issues that plagued NTFS. For example, disks formatted with NTFS require an administrator to manually run the chkdsk utility to check and repair disk errors. The reality of modern multi-terabyte storage arrays makes it impractical to take storage resources offline for granular, time-consuming troubleshooting sessions. Enterprises on storage hardware that use NTFS have adapted to its shortcomings by purchasing systems that provide data protection, integrity checking and redundancy.

Microsoft ReFS includes native features, including automatic integrity checks and data scrubbing. A system that runs on ReFS takes corrective action before an error manifests; it's particularly effective when businesses use ReFS on mirrored (RAID 1) or parity (RAID 5 or RAID 6) volumes. These self-healing properties eliminate the need to run disks through a chkdsk maintenance schedule.

Microsoft ReFS works in conjunction with Storage Spaces -- the software-defined feature that builds storage pools -- to duplicate data during disk writes for better data resilience without a separate copy process. Microsoft ReFS supports long paths and file names, and it adds better support for storage virtualization and pooling -- critical for software-defined data centers.

Storage Spaces Direct a key
Windows Server 2016 feature

In this podcast, Brian Posey, a Microsoft MVP and frequent TechTarget contributor, explains the storage features in Windows Server 2016, including Storage Spaces Direct, Storage Replica and Resilient File System.

In addition to the protection measures, Microsoft ReFS received several enhancements to improve storage performance in Windows Server 2016, which include high-speed redeploying, reordering and cloning of blocks between files. Block cloning is particularly effective for virtualization to supply faster provisioning, file merges and storage performance tiering.

Microsoft ReFS in Windows Server 2016 includes parallelization, monitoring of unallocated space and a redo log for synchronous disk writes. The 2016 version collects small random writes and commits them to disk as a single larger write, which is far more efficient on I/O, targeting highly virtualized systems that can compete for storage I/O.

Limitations of Microsoft ReFS

ReFS can help organizations with large storage volumes improve resilience and performance.

ReFS handles a maximum volume size of 1 yobibyte -- equivalent to 1.2 trillion terabytes -- and supports a maximum file size of 16 exbibytes -- or 1.1 million terabytes. Despite these advantages over NTFS, administrators should be aware of some limitations before Microsoft ReFS enters production.

Windows cannot boot from a ReFS volume. A Windows Server 2016 system needs an NTFS volume to boot and then uses the ReFS volumes for workload storage. ReFS also abandons some commonplace NTFS features such as traditional 8.3 filename structures, compression, Encrypting File System, extended attributes and disk quotas.

ReFS does not use data deduplication and Microsoft only added support for alternate data streams up to 128 KB with Windows 8.1 and Windows Server 2012 R2. ReFS is also unsuitable for removable storage devices.

A Microsoft ReFS volume could become inaccessible in certain scenarios. For example, a thin-provisioned ReFS volume can fail when used with Storage Spaces if the physical disks are near capacity. Also, because Storage Spaces handles blocks and ReFS handles files, ReFS might not reliably recover file errors.

Advantages of Windows Server 2016
and ReFS for a backup repository

In this video, Clint Wyckoff discusses why an organization might consider Microsoft's Resilient File System for backup storage. Recorded at TECHunplugged in Chicago on Oct. 27, 2016.

Microsoft designed ReFS without tools for ReFS volume repair or recovery. If a fault occurs, the only option is to restore from a backup.

ReFS might not suit all data center tasks. Workloads or utilities that depend on NTFS capabilities might not work properly on ReFS volumes. For example, Windows Deployment Services requires NTFS to operate.

Microsoft ReFS future and appropriate uses

Until Microsoft can add key functionality, such as the ability to boot into Windows with an ReFS volume, ReFS might remain a niche technology. Administrators can use it for storage tasks where the file system's unique benefits, such as resiliency and performance improvements, would be most effective -- especially for virtual machines.

Currently, Microsoft ReFS is perhaps the best match for deployment scenarios that use Storage Spaces Direct, a feature in the Datacenter edition of Windows Server 2016 to build high-availability clusters with local direct-attached storage. Highly virtualized environments that use Hyper-V would benefit from using ReFS because of the performance optimizations for virtual hard disk and VHDX VMs.

While ReFS can be a solid foundation for many workload deployments based on Hyper-V, the lack of deduplication support might cause some organizations to avoid ReFS. In a VDI deployment that needs storage deduplication, expect to use NTFS.

The data integrity features of ReFS suit archival storage well. ReFS coupled with Storage Spaces provides even greater resiliency for critical, long-term data storage tasks.

ReFS isn't a fit for everything. It doesn't work on domain controllers; Microsoft does not recommend using a ReFS volume to store an Active Directory database, log files or the sysvol folder that resides on each domain controller within the domain. SQL Servers administrators can't run tools such as DBCC CHECKDB or generate snapshots.

Next Steps

Is Microsoft ReFS a replacement for data backup?

The administrator's essential guide to Windows Server 2016

Storage Spaces Direct is an inexpensive storage option

Dig Deeper on Windows Server storage management