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Choose 4. System Control; then
Then choose 3. Stop storage processes.
Confirm that choice by choosing Yes.
At that point, you should see Storage Processes: STOPPED
Then choose 2. Disk Volumes
Arrow down to the disk in question and press "f"
The prompt will ask you to type: FORMAT to continue. There is no formatting actually taking place at this point, so do not expect a delay. The disk is being marked for re-format on next boot.
At that point, you can reboot the system under System Control.
The disk will be reformatted as the chassis mounts.
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