HSZ70 controllers and formatting disks

Hi I am trying to format all the disks in several of my old dec-alphas and unix boxes. I have connected to the hsz70 controller and used "run hsutil" command but when i select the "format" option, the response i get is "no available unattached devices to format" Does anyone know how I can 'unattach' the disks to get them ready for formatting? Cheers :confused: