On Thu, Nov 28, 2013 at 8:39 AM, Charles Dickman <chd at chdickman.com> wrote: The MSCP unit number assignment is controller specific. It can be set with the built in configuration utility on the CMD CQD-223. On the RQDX3 it is set by configuration jumpers on the controller. http://www.bitsavers.org/pdf/dec/qbus/fiche/EK-RQDX3-UG-001_Nov85.pdf Page 2-2 Starting LUN The starting LUN equals the binary number represented by jumpers W12 (LSB) through W17 (MSB) multiplied by 4. When jumpers W12 through W17 are removed as shown in Figure 2-2, a starting LUN of 0 is selected. Refer to Table 2-1 for typical examples. Most likely in your case with the RQDX3 configured as the secondary MSCP controller you would want a jumper installed at W12 so the RQDX3 drives start at MSCP unit number 4.