CLAYTON@XRT.UPENN.EDU ("Clayton, Paul D.") (02/07/88)
Regarding the question of using one or two KDB50 controllers to connect RA82's I offer the following thoughts. The use of the KBD50 , for BI connection of RA type disks, is sound and one of few choices available. The connection of four RA82's or one SA482 is mute due to they being equivelant, except for packaging. The remaining problem then is one or two channels to the disks. With the KDB type interface you would indeed be accessing the disks in parallel if two KDB interfaces were used. Please understand that the accessing is essentially parallel, but any data transfer is single threaded, as the BI does not allow concurrent bus masters. Documentation I have read leads one to think that having several BI buses/channels connected up to the same processor could in fact give true concurrent access to devices on the different buses. I do not have a machine configured like this so I can not prove/disprove the theory. Anyway, the KDB/UDA has some smarts, but not as much as a HSC controller, in queueing requests to a disk drive. The bottom line is that it is a win situation when you can dedicate controllers to single devices, for the most part. The overall performance/throughput tends to decrease when more devices are placed on a controller. Remember that the throughput information for any given controller is an AGGREGATE amount of ALL used inputs. Paul D. Clayton - Manager Of Systems TSO Financial - Horsham, Pa. USA Address - CLAYTON%XRT@CIS.UPENN.EDU