Microsoft will begin blocking certain USB drives and other external storage devices formatted with its Resilient File System (ReFS) from mounting on supported Windows platforms starting in January 2027.
The change is part of a security update designed to restrict unsupported storage configurations. Microsoft says ReFS is not intended for removable media, including USB disks, and the new measures will help administrators identify affected devices and prevent them from being mounted.
Blocking to begin in January 2027
Microsoft introduced the changes through a security update released on October 13, 2026, initially enabling auditing rather than blocking. This allows administrators to identify ReFS-formatted external drives and assess whether their systems rely on them.
With the January 2027 security update, auditing and blocking will be enabled by default. Affected volumes will no longer mount unless an administrator explicitly changes the relevant policy setting.
Microsoft’s documentation says administrators can monitor Windows system logs for warning events identifying ReFS volumes connected to removable or externally attached storage. The company also recommends moving data and workloads to supported storage configurations before enforcement begins.
Most consumer USB drives should be unaffected
The restriction is unlikely to affect most everyday users because consumer USB drives and external hard drives commonly use NTFS, FAT32, or exFAT. The change specifically targets external volumes formatted with ReFS.
However, users who rely on ReFS-formatted external storage could lose access to their files through Windows once blocking takes effect. Microsoft says the policy does not itself delete the data, but users should ensure important files are available on supported storage before the deadline.
Administrators can control the restriction
Microsoft is introducing a Group Policy and registry setting to manage how Windows handles ReFS volumes on removable devices. Administrators can configure it to turn the feature off, enable auditing or block affected volumes. Group Policy takes precedence when both policy and registry settings are configured.
The phased rollout gives organisations time to identify affected drives, test their applications and migrate necessary data before the new default enforcement begins.
For most Windows users, no action should be necessary. Those using ReFS on external drives, however, should check their storage format and prepare to move their data before January 2027.
Source: Microsoft