2. Type: diskpart
3. At the DISKPART prompt, type: list disk.
Write down the disk number of the lost or offline disk for online. The lost disk numbers are M0, M 1, M2, etc. , and the number of offline disks is 0, 1, 2, etc.
4. at the DISKPART prompt, type: select disk n.
5. At the DISKPART prompt, type: online.