When looking in Event Viewer, One of our target servers has the Storage Diagnostics log folder named Microsoft-Windows-Storage-ClassPnP/Operational having repeated Errors (Event ID 504) with the message 'Completing a failed IOCTL request'. Has anyone else seen this in their server logs? Our target server is working correctly and collecting data but this error repeats about 20 times in a five minute period of time. Error Source: StorDiag. Keywords: Device I/O control request.