Microsoft has announced a significant shift in its approach to external storage devices, specifically those formatted with the Resilient File System (ReFS). Starting in January 2027, Windows will block ReFS-formatted USB drives and external storage devices by default. This decision is part of a broader initiative aimed at enhancing the security of the operating system. The change will impact Windows 11, supported Windows 10 installations, and Windows Server, although the majority of users are unlikely to notice any immediate effects.
As outlined in an official Microsoft support document released on October 13, 2026, the company is implementing new restrictions on how Windows interacts with removable storage devices formatted with ReFS. For those who may not be familiar, ReFS is a relatively modern file system developed by Microsoft, primarily intended for enterprise and server environments. It boasts several advantages over the more commonly used NTFS (New Technology File System), including enhanced data integrity, improved resilience against corruption, support for very large volumes, and features like block cloning that can significantly speed up certain file operations.
Microsoft Is Tightening Security Around ReFS
While Microsoft has expanded the use of ReFS beyond servers—most notably through the introduction of ReFS-based Dev Drives in Windows 11 to enhance performance for development workloads—it’s important to note that ReFS has never officially supported removable storage devices such as USB flash drives and external HDDs or SSDs. Although Windows has typically allowed users to mount these volumes, the company is now moving to restrict these unsupported configurations.
The rollout of this change will occur in two phases:
- October 13, 2026: The initial security update will introduce auditing by default, allowing Windows to record affected ReFS volumes in the Event Viewer under Event ID 524 while still permitting them to mount.
- January 2027: The enforcement phase will commence, with Windows automatically preventing affected ReFS volumes from mounting unless an administrator explicitly overrides this restriction.
Importantly, this change will not erase the contents of affected drives. However, users may find themselves unable to access their files through Windows once the restrictions take effect. Microsoft has stated that this decision aims to reduce exposure associated with unsupported storage configurations, although no specific vulnerabilities have been identified as the catalyst for this change.
Here’s What Affected Windows Users Can Do
Fortunately, the upcoming changes should have minimal impact on the average consumer. Most USB flash drives and external storage devices utilize FAT32, exFAT, or NTFS, none of which are subject to this particular restriction. However, those utilizing ReFS-formatted external storage should consider transferring their files to a supported format before January 2027. Users can easily check their drive’s file system through the Properties menu in Windows File Explorer.
For advanced users and system administrators, Microsoft has introduced a configurable registry and Group Policy setting known as RefsRemovableDeviceMountPolicy. This setting supports three values: 0 disables the restriction, 1 enables auditing, and 2 blocks affected volumes. Any configuration changes will require a system restart, with Group Policy taking precedence over local registry settings.
While Microsoft does provide a method to override the restriction, migrating affected workloads to supported storage remains the recommended long-term solution. For most Windows users, the changes set for January will likely go unnoticed. Nevertheless, enthusiasts and administrators who rely on ReFS-formatted external drives should take proactive measures to avoid unexpected accessibility issues.
News Source: Microsoft
About the author: Sebastian Castellanos is a data scientist by education and training. He’s also deeply passionate about PC gaming hardware and software. He has recently started writing technical articles and guides on Wccftech about PC hardware, games, and mods.
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