Disk Xfer Rates vs Bus Speed

[markb at denali]

In article <3877 at encore.UUCP>, terryk at pinocchio.Encore.COM (Terence Kelleher) writes:
> ESDI is an easy winner, if you compare 1 disk to 1 disk.  If you are
> using more disks, SCSI provides the nice features of overlapped
> operations.  2 disks, with seperate controllers, on the SCSI bus will
> provide very near twice the throughput of 1 drive.  This is not the
> case with ESDI.  Which is better really depends on wheter you care
> more about overall throughput or single access times.
> 

The more sophisticated ESDI and SMD controllers are actually much
faster than multiple embedded SCSI's on a single bus, too.  That is,
they support overlapped seek operation, command sorting, command
queuing, seek optimization, and they have look-ahead, buffering
and very fast fifo's.  They will also support scatter-gather operation
which tends to help us considerably, as you might expect.

Some of my comparisons on SCSI, ESDI, and SMDE are below on our product.
These are on read performance through the EFS.

SCSI:  450 KBS (async, single ended, 10 MHz drive)
ESDI:  980 KBS (with above features, 10 MHz drive)
ESDI: 1500 KBS (with above features, 15 MHz drive)
SMDE: 2100 KBS (with above features, 24 MHz drive)

these numbers actually look better on an AIM benchmark, but this BM tends
to provide varibale results that skew upward in many cases.  As one would
expect, the file system tends to slow things a bit, and of course multiple
drives would up the throughput considerably in all cases.  

Mark Bradley				"Faster, faster, until the thrill of
Manager I/O Subsystems			 speed overcomes the fear of death."
Silicon Graphics Computer Systems
Mountain View, CA			     ---Hunter S. Thompson