Disk Xfer Rates vs Bus Speed

[Green Eric Lee]

In article <3899 at encore.UUCP> terryk at pinocchio.UUCP (Terence Kelleher) writes:
>In article <20606 at sgi.SGI.COM> markb at denali writes:

>>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)

Recently someone was rattling on comp.sys.amiga about how it was
impossible to get 500KBS out of a particular SCSI interface. Several
people replied that yes, they did -- going through the operating
system, no less. 
   One particularly interesting statistic was that for 32kbyte
transfers, they averaged 850Kbytes/second. (Note that AmigaDOS lets
you issue file system requests as large as available contigious
memory). This was with a Commodore Amiga, AmigaDOS, Fast File System,
CDC Wren drive, and, uhm, I think it was the Great Valley Products
SCSI interface.

>>expect, the file system tends to slow things a bit, and of course multiple

Virtual memory also tends to slow things a bit, since your OS has to
do a bit of trickery to make sure the disk buffer is mapped into your
process address space, or else it has to do some data copying (Unix
does copying, I believe, due to its caching algorithm). Not to mention
that the traditional Unix inode/block organization is ridiculous
(unless you were using BSD4.x), and Unix tasks are very heavy-weight
(the Amiga has a real-time kernal). Unix probably is not a very good
benchmark for measuring I/O performance....

--
Eric Green                               P.O. Box 92191, Lafayette, LA 70509
{ames mit-eddie etc.}!killer!elg, killer!usl!usl-pc!jpdres10, etc. etc. etc.