Multiple disks per IO channel?

     All Oracle documentation that I have seen indicates that every drive
should be on its own IO channel, which for PC servers involves a great deal of expense. I understand that having only one drive per channel would
be best, but that seems to me to be severe overkill.

      At what point do multiple IO channels make a difference? How many

drives, how fast drives, what kind of transactions, etc? In our case we

will have four 4GB 10K rpm drives configured as two RAID 1 pairs. Given

that the RAID bus connected to the four drives is an Ultra SCSI bus, as I understand it the RAID bus throughput then is 80 megabytes/sec. Since

each of the drives maxes out around 15MB/sec it would seem that the bus has sufficient headroom even with all four drives operating at full speed. However there may well be complications, for example can or will

one drive tie up the bus for an extended period of time, thereby locking

out the other drives? If a lengthy transaction, such as 0.1-1.0 seconds, is initiated do the other drives have to wait until it completes?

     I realize there may not be clear-cut answers to the above but I would appreciate any feedback or guidelines that are available.

    Thanks in advance.

Aaron Buhr
ambuhr_at_southeast.net Received on Tue Jul 07 1998 - 17:20:20 CDT