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From: lfernand@cc4.bbn.com.BBN.COM (Louis F. Fernandez)
Newsgroups: comp.arch
Subject: Re: Re: Disk Striping
Message-ID: <310@cc4.bbn.com.BBN.COM>
Date: Fri, 7-Aug-87 08:44:32 EDT
Article-I.D.: cc4.310
Posted: Fri Aug  7 08:44:32 1987
Date-Received: Sun, 9-Aug-87 07:08:24 EDT
References: <582@saturn.ucsc.edu>
Organization: Bolt Beranek and Newman, Cambridge, MA
Lines: 27

> 
> Isn't this what IBM uses in their Airline Control Program?  There was that
> article in CACM a while back about the TWA reservation system, and it said
> something about spreading files over a large number of spindles for greater
> throughput.
> 
> haynes@ucscc.ucsc.edu

What ACP does isn't what we are calling disk striping in this newsgroup.
ACP has an option to write each record to two different disks at the same
time.  This doesn't increase throughput but does has several benefits:

    1/ It creates a backup copy so the data will not be lost if one disk
       crashes.
    2/ It allows ACP a choice of where to read the data from.  ACP will
       read the data from the disk with the shortest queue, reducing the
       access delay.

BTW, airline reservations systems have quite high performance.  Large ones
(e.g., United and American) average over 1000 transactions per second,
where a transaction is a few characters of keyboard input, a half-dozen
disk access, and a few hundred characters of CRT output.  

...Lou

lfernandez@bbn.com
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