Twice in the past month my main data drive array has stopped responding, and Windows has dropped it. It's two 4TB drives, formatted ReFS, in a storage spaces mirror, plugged into two SATA ports on the motherboard. Windows 10 pro, up to date. Gigabyte motherboard. Any ideas of the cause or diagnosis steps? I'm about to run the driver verifier. 

Here are the event viewer messages I could find that look related.

ReFSv1: The file system was unable to write metadata to the media backing volume R:. A write failed with status "A device which does not exist was specified." ReFS will take the volume offline. It may be mounted again automatically.

Can't remember source: The driver \Driver\WudfRd failed to load for the device SWD\WPDBUSENUM\_??_USBSTOR#Disk &Ven_Generic& Prod_STORAGE_DEVICE &Rev_9451#7&2a9fd895&0#{53f56307-b6bf-11d0-94f2-00a0c91efb8b}.

DbxSvc: "Failed to connect to the driver: (-2147024894) The system cannot find the file specified. "