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Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!purdue!decwrl!shelby!polya!kaufman
From: kaufman@polya.Stanford.EDU (Marc T. Kaufman)
Newsgroups: comp.periphs,comp.sys.mac
Subject: Re: Impulse drives from Quantum/Plus
Message-ID: <7657@polya.Stanford.EDU>
Date: 13 Mar 89 05:50:33 GMT
References: <1397@ccnysci.UUCP> <379@siswat.UUCP>
Sender: Marc T. Kaufman <kaufman@polya.Stanford.EDU>
Reply-To: kaufman@polya.Stanford.EDU (Marc T. Kaufman)
Followup-To: comp.periphs
Organization: Stanford University
Lines: 20

In article <379@siswat.UUCP> buck@siswat.UUCP (A. Lester Buck) writes:
>I didn't read the Infoworld article, but does this guy work for 
>the company making Cluster Disk Interfaces?  He sure doesn't
>understand SCSI...

>            ...It turns out that the Unix buffer cache search is
>about 30% of the total transfer overhead today, and the
>requirement that the target check every bit of the SCSI
>command data block parameters for validity is another 30%
>or so...

Huh?  The command data block is 6 bytes long.  The only parameter of any
consequence in it is the sector address.  How can this take 30% of the transfer
time?  The Mac II SCSI interface peaks at 1.4 MB/sec transfer rate.  The SE can
get 600 KB/sec.  Using the Device interface on a IIx, I get 330 KB/sec
sustained on Apple's HD 80, and 450 KB/sec on a new SuperMac drive.  As this is
a continuous read through 80 MB of disk, the cache is of no consequence in
these numbers.

Marc Kaufman (kaufman@polya.stanford.edu)