davis@clocs.cs.unc.edu (Mark Davis) (06/06/89)
What is the performance of 8 bit SCSI controllers running SCSI hard disks in real systems? This question came up because of the large number of Seagate "matched pairs" on the market. My favorite right now is the ST296N 80 meg drive with ST01 SCSI host adapter. At mail order prices of under $600, this is a pretty good deal considering you get the controller too. But what is the transfer rate really? If this type of setup is a real dog, it may be better to go with other arrangements. The controller can handle 1:1 interleave and disk to controller transfer rates of up to 10 Mbits/sec. The ST296N has 34 sectors per track, 512 bytes per sector and rotates at 3600 RPM. Multiply this all together (and adjust units) and you get 1,044,480 bytes per second transfer rate. I don't think an XT can go that fast (at 4 cycles per access and two accesses to transfer data, I get the maximum bus transfer (really copy from point to point) rate to be about 500,000 for a 4 MHz XT). By similar calculations, I get an 8 Meg AT with a transfer rate of about 4 Megabytes transferred per second (2 cycles per access and 2 bytes per access). With 8 bit transfers, you are down to 2 Meg/sec so, can an AT compatible really move 1,044,480 bytes per second in 8 bit quantities from this controller? Please note that many of the hard cards out today are ST01's with a 3.5" Seagate drive attached (Shamrock has a whole line of them). The Seagate 3.5" SCSI drives all use 26 sectors per track, so their maximum theoretical transfer rate is 798,720. If anybody has the transfer rate numbers for any SCSI drive and especially 8 bit SCSI controllers, I am very interested. Please identify the drive and controller and don't forget HZ and type (AT or PC) of your computer. please mail them to me: davis@cs.unc.edu uunet!mcnc!davis decwrl!mcnc!davis If mail bounces or is hard, go ahead and post, but I will summarize all results that get mailed to me. The most robust program I know for measuring transfer rate is SPINTEST. Gibson research freely distributes it to try to sell their real product, SPINRITE. If you have a SCSI controller, but not a program that will measure transfer rate, I will gladly mail you SPINTEST (or you can get it from simtel in pd1:<msdos.dskutl> as SPINTEST.ARC). Simtel also has CORE281.ARC,Core Hard Disk Evaluator - v2.81, and other programs that will do the job. Thanks - Mark (davis@cs.unc.edu or uunet!mcnc!davis)