This Ruby example detaches a disk from a virtual machine.

# Find the virtual machine:
vm = vms_service.list(search: 'name=myvm').first

# Detach the first disk from the virtual machine:
vm_service = vms_service.vm_service(vm.id)
attachments_service = vm_service.disk_attachments_service
attachment = attachments_service.list.first

# Remove the attachment. The default behavior is that the disk is detached
# from the virtual machine, but not deleted from the system. If you wish to
# delete the disk, change the detach_only parameter to false.
attachment.remove(detach_only: true)

For more information, see http://www.rubydoc.info/gems/ovirt-engine-sdk/OvirtSDK4/VmService:disk_attachments_service.