anchor.diff:          %% LUMA API Key, must be identical with API Key in external LUMA
           %% service.
           lumaApiKey => {string, optional},
  -        %% The type of storage.
  -        type => {equal, <<"posix">>},
           %% The absolute path to the directory where the POSIX storage is mounted
           %% on the cluster nodes.
           mountPoint => string,
  
positive.code:         %% LUMA API Key, must be identical with API Key in external LUMA
          %% service.
          lumaApiKey => {string, optional},
          %% The type of storage.
          type => {equal, <<"nulldevice">>},
          %% Minimum latency in milliseconds, which should be simulated for
          %% selected operations.
          latencyMin => {integer, optional},
  
negative.code:         username => string,
          %% The user role, one of `admin` or `regular`.
          userRole => atom,
          %% List of cluster privileges held by the user. This field is returned
          %% only to a Onezone user fetching information about himself.
          clusterPrivileges => {[string], optional}
      }.
  
  