Try removing the device from the USB Port then go back into Storage Spaces and click on remove or Change Settings if it isn't still greyed out. Once you've reconnected the drive and made sure your data are all intact, you could reset the drive and put it back into Storage Spaces.
Try removing the device from the USB Port then go back into Storage Spaces and click on remove or Change Settings if it isn't still greyed out. Once you've reconnected the drive and made sure your data are all intact, you could reset the drive and put it back into Storage Spaces.