Mounting and Dismounting Volumes
You can mount and dismount volumes from the command line with the mountvol.exe command. On basic disks, if you type mountvol x: /p, where x: represents the volume's drive letter, you can dismount a volume and take it offline.
The /p parameter is not supported on dynamic disks. The command mountvol x: /l displays the specified drive letter's volume ID. By using the syntax mountvol x: volume_ID, you can assign a drive letter to the volume and remount it to bring it back online, eg: the command:
would assign drive letter S: to the specified volume.
You can also use Disk Management to mount and dismount volumes from the GUI. You can mount and dismount volumes by right-clicking a volume and selecting Change Drive Letter and Paths. By removing the drive letter and any other paths (mount points) for the volume, you take the volume offline.