To configure for writing and "on the fly" copying, you would put the the writer on it's own as Secondary Master, the hard disk stays as Primary Master, and the DVD-ROM as Primary Slave.
(good for drive to drive on the fly, good for HD to writer, not optimal for DVD-ROM to HD).
The Alternative layout, with the DVD-ROM as secondary slave, is sub-optimal for DVD-ROM to writer direct "on the fly" copying, but is optimal wher that data is buffered to HD - either as an option in the copy, or by making and then writing an image file.
The old rule:
A writer does not share an IDE with it's write source, or with any other drive that will be in use during writing.
The ideal path is from a source drive on one IDE, to a destination on the other, and minimal other traffic - burnproof means that deviations from this will no longer mean a burn-fatal underrun, and improvements to software and drive buffer management may have alleviated the worst of the old problems.
Some software, did little buffer management with the writer, and merely stuffed the writer's buffer until busy (jamming the IDE, and crucifying the performance of any other drive on the same cable). If buffers are managed better, then the "lock out", problem is avoided, by feeding data to the writer only when it has buffer space available.