From inSync reader "plhead" comes another SCSI suggestion:
Because the Mac OS scans the SCSI chain from high to low ID #, always put, when possible, the slowest, and/or least priority drives, on the lowest ID #’s on the chain.
Thanks "pl" – This means that in practical terms, the drives that require the fastest access should be put on the higher ID’s. For example, it would make sense to put an external drive used for audio at ID #6 (The Mac always takes #0 and #7 for itself and its internal hard drive) a CD-R might be placed at #5, etc.