macOS 10.13's Disk Utility 17.0 (1626) does not recognize raw drives, reads a blog post, shared by several readers. From the post: Diskutil does recognize the drive. We'll use it to perform a quick, cursory format (e.g., diskutil eraseDisk JHFS+ NewDisk GPT disk0) to make the disk appear in Disk Utility, where further modifications can more easily be made. Plugging in an unformatted external drive produces the usual alert, "The disk you inserted was not readable by this computer. Initialize... | Ignore | Eject", but clicking Initialize just opens Disk Utility without the disk appearing. There's an option in Disk Utility to view "all devices," but clicking that doesn't show raw disks, the blog post adds.