Starting in January 2027, Windows will block ReFS-formatted USB drives and external storage devices by default as part of a security initiative. This change will affect Windows 11, supported Windows 10 installations, and Windows Server. The rollout will occur in two phases:
1. On October 13, 2026, an initial security update will introduce auditing for affected ReFS volumes, allowing them to mount but recording them in the Event Viewer.
2. In January 2027, Windows will prevent affected ReFS volumes from mounting unless overridden by an administrator.
This change will not erase the contents of affected drives, but users may lose access to their files. Microsoft has stated that this move aims to reduce exposure associated with unsupported storage configurations. Most users are unlikely to notice immediate effects, as common USB drives use FAT32, exFAT, or NTFS, which are not subject to this restriction. Users with ReFS-formatted external storage should consider transferring their files to a supported format before the deadline. Additionally, Microsoft has introduced a registry and Group Policy setting, RefsRemovableDeviceMountPolicy, to allow for configurable restrictions.