bsk@cbnewsi.att.com (barry.s.kizmann) (06/30/90)
This is the first time I am posting to this group, so I hope it is the correct
one. I have a question about SCSI vs. ESDI. A friend of mine just acquired
a Data General AViiON 5000 Unix Server. He has to decide whether to use
ESDI, SCSI or both drives. It will be the same drive for either controller so
seek time, rotational latency, and head transfer rate don't matter. They both
also use the same VME bus.
The following describes the ESDI:
VME/ESDI Controller (equivalent to the Ciprico RimFire 3400)
National 8466 Disk Data Controller Burst rates w/disk of up to 2.5Mb/sec
3ms controller overhead w/80186 processor
Segmented read-ahead Cache (512Kb)
Reduced latency operations
The following describes the SCSI:
VME/SCSI Host Adaptor (equivalent to the Ciprico Rimfire 3513)
Synchronous and Async modes through WD 33C92 chip supporting 5Mb/sec
and 1.5Mb/sec respectively
3ms controller overhead w/80186 processor
Each one also has:
Overlapped seekds
Command Queueing for each unit in 64Kb memory
Command Optimization
Command Coalescing
Scatter/Gather operations
He has two drives and in the future may be getting a third. His applications
are written in COBOL and use some type of ISAM layout, so he expects to be
doing lots of transfers of small records. The applications are typical of a
small business, payroll, billing, customer info, etc.
Does anyone have any insight to what combination to get, or does it even matter.
Greg Romer romer@csd5.nyu.edu or romer@spunky.cs.nyu.edujackw@hpdmd48.HP.COM (jack wood) (07/12/90)
>I have a question about SCSI vs. ESDI. A friend of mine just acquired >a Data General AViiON 5000 Unix Server. He has to decide whether to use >ESDI, SCSI or both drives. It will be the same drive for either controller so >seek time, rotational latency, and head transfer rate don't matter. They both >also use the same VME bus. There is a big difference between the performance of multiple disk configurations of SCSI and ESDI. For a really good article on the subject, see MIPS Magazine (now called Personal Workstation), June 1989. The machine tested in that article was an 80386-based machine running SCO Xenix, but I think that the results can be extrapolated to your configuration. In the article, benchmark data is presented showing that the ESDI disk and the SCSI disk being tested had about the same performance in a single disk configuration. However, as more disks and more processes were added to the test, the SCSI disk system far outpaced the ESDI system. The reason for that is that the ESDI disk will hold the channel while it is performing a seek, while the SCSI disk will disconnect, letting another disk use the channel. I think that your friend would be much better off using the SCSI interface. >He has two drives and in the future may be getting a third. His applications >are written in COBOL and use some type of ISAM layout, so he expects to be >doing lots of transfers of small records. The applications are typical of a >small business, payroll, billing, customer info, etc. > >Greg Romer romer@csd5.nyu.edu or romer@spunky.cs.nyu.edu __ | | | | | | \ | / \ | \ | ---| | | | . | |---------- Jack Wood Hewlett-Packard Boise, ID 208-323-4529 "The opinions expressed above may or may not be the opinions of my employer"
taylor@anthrax.Solbourne.COM (Dick Taylor) (07/13/90)
In article <15370004@hpdmd48.HP.COM> jackw@hpdmd48.HP.COM (jack wood) writes: > >>I have a question about SCSI vs. ESDI. A friend of mine just acquired >>a Data General AViiON 5000 Unix Server. He has to decide whether to use >>ESDI, SCSI or both drives. It will be the same drive for either controller so >>seek time, rotational latency, and head transfer rate don't matter. They both >>also use the same VME bus. > >There is a big difference between the performance of multiple disk >configurations of SCSI and ESDI. For a really good article on the subject, >see MIPS Magazine (now called Personal Workstation), June 1989. The machine >tested in that article was an 80386-based machine running SCO Xenix, >... > >The reason for that is that the ESDI disk will hold the channel while it is >performing a seek, while the SCSI disk will disconnect, letting another >disk use the channel. I think that your friend would be much better off >using the SCSI interface. > Actually, seeks are overlapped on the Ciprico controller (a version of which is used in the AViiON). Experience gained on an AT-bus '386 is unlikely to be valid when extended to cover VMEbus workstations. ESDI is usually faster because the controller handles its cache better than the drives do (with these controllers and disks, anyway). SCSI also has higher per-command overhead (adding the drive overhead and the HBA overhead, plus things like disconnect times). As SCSI develops and as the new drives become available in workstations, SCSI will end up having an edge in many applications. This will happen because SCSI should continue to hold a cost advantage and the limiting disk performance is the same -- the speed of the drive. SCSI is also better-poised to head for drives beyond 24MHz and technologies like ZBR. As far as a recommendation goes, I'd suggest that your friend try to get a chance to benchmark his applications on a machine configured with both ESDI and SCSI. It's really the only way to know whether it makes a difference for him. NOTE: The foregoing is based on personal experience with Ciprico and its products, but does NOT represent the opinions of either Ciprico or Data General. If they want to say something, they will say it themselves.