For a 34xx or 35xx tape device attached to a SCSI I/O adaptor (IOA), you must set the SCSI address to 0 when the device is used for an initial program load (IPL). The SCSI address can be set to any address except 7 when the device is not being used for an IPL.
For a 34xx tape device attached to a type 2644 IOP, you must set the controller address to address 7. The device address must be set to address 0 when the device is used for an IPL. You can use address 8 when there is no device at address 0. You can set the controller and device to any value when the device is not being used for an IPL.