backup SSD disks suddenly not mounting -
Recently purchased four 2T SSD drives to backup other external USB drives. Yesterday drives showed on desktop and each directory was as expected. Today none of the drives will mount. Thought there might be a USB issue with my MacPro. So, tried connecting to MacBook but same problem. Attached one drive to an internal tray and rebooted but still no mount. Suggestions are greatly appreciated!
Mac Pro, macOS 10.14