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ERROR_DAX_MAPPING_EXISTS
Active DAX mappings keep the volume in use
ERROR_DAX_MAPPING_EXISTS is a Win32 system result. A process has memory mapped persistent storage through DAX. Operations such as dismount, reconfiguration, or maintenance cannot proceed while those mappings remain active.
What the result means
The volume still has active direct-access mappings that prevent the requested operation. For ERROR_DAX_MAPPING_EXISTS, keep the symbolic name, numeric value, and failing operation together in diagnostics; that combination distinguishes the exact failure path from nearby system results.
What to check
- Identify processes that hold mappings or open handles to the volume.
- Stop application access through its normal shutdown or quiesce mechanism.
- Account for services, background agents, and stale worker processes.
- Verify that mappings are actually released before retrying volume operations.
Recommended handling
Coordinate application shutdown, unmap views, close handles, and then retry. Avoid terminating processes without understanding persistent-memory consistency and recovery requirements.
Developer notes
Design DAX users with explicit quiesce and maintenance hooks. Track mapping lifetime deterministically and flush required data before unmapping. When a Win32 API reports ERROR_DAX_MAPPING_EXISTS, capture GetLastError() immediately; subsequent cleanup, formatting, or logging calls can replace the thread-local value.
References
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