Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rutgers!princeton!rocksvax!martyl
From: martyl@rocksvax.UUCP (Marty Leisner)
Newsgroups: comp.unix.wizards
Subject: Re: Berkeley FFS and SCSI
Message-ID: <1142@rocksvax.UUCP>
Date: Mon, 1-Jun-87 16:29:34 EDT
Article-I.D.: rocksvax.1142
Posted: Mon Jun  1 16:29:34 1987
Date-Received: Wed, 3-Jun-87 02:22:14 EDT
References: <16753@amdcad.AMD.COM> <324@forbrk.UUCP>
Reply-To: martyl@rocksvax.UUCP (Marty Leisner)
Organization: Xerox: Henrietta, NY
Lines: 33

In article <324@forbrk.UUCP> mats@forbrk.UUCP (Mats Wichmann) writes:
>SCSI is an essentially low-performance peripheral interface. Its' main
>advantage is ease of integration of new peripherals. 

I was under the impression SCSI could transfer data at several megabytes/
second (1.5-4? depending on whether it is asynchronous or synchronous?)  
This sounds pretty high performance to me.  What CPU can eat data that
fast?

>My biggest problem with SCSI is that you are too far removed from the disk. 
>I would *like* my disk controller to buffer lots of data, and preferably 
>to keep reading stuff and storing it away while there are no other requests 
>pending (non-intrusive readahead). 

Is this a problem with the interface or the boards being built for it?


If caching is done on both ends (host adapter and disk controller) and with
a low performance microprocessor on each end, it looks like impressive
performance could be achieved.  Whenever a read request is made to disk,
the process needing the data has to hang on the disk access anyway -- once
the request is initiated, the host cpu shouldn't be bothered with the 
pending request until it receives acknowledgement the operation is complete.
From a device driver point of view, I like to pass linear sector numbers to
the controller and let the controller figure out the head/track/sector.  

Also, SCSI appears to have the capability to do interesting things with multiple hosts sharing multiple disks (I'm thinking of buying a SCSI disk for my PC AT
at work).  

marty leisner
xerox corp
leisner.henr@xerox.com
martyl@rocksvax.uucp