Path: utzoo!attcan!uunet!snorkelwacker!think!ephraim
From: ephraim@think.com (Ephraim Vishniac)
Newsgroups: comp.sys.mac.hardware
Subject: Re: DiskTimer II times?
Message-ID: <34620@news.Think.COM>
Date: 13 Mar 90 15:06:45 GMT
References: <1944@naucse.UUCP>
Sender: news@Think.COM
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 46

In article <1944@naucse.UUCP> rrw@naucse.UUCP (Robert Wier) writes:
>I recently was running some disk drive benchmarks using disktimer II, V1.0
>and got the following:

>             HD20SC       Wren Runner       Quantum 40      
>             (external)     (external)       (internal)
>Reads          97             16                31
>Writes         96             16                29
>Access         33              5                 0

>misc info  Seagate 225N   CDC 94181-15        P40S V9.6
>                           V. 7980
>Note that Reads is time for 100 24kb reads in deciseconds, Writes is 
>similar for write times, Access is time for 80 1kb seeks.

>Now, that Quantum access is fast, don't you think?

>Can anyone make some suggestions as to why the seek times seem to be
>somewhat off?

***************************************************************************
* Don't accept benchmark results unless you know how the benchmark works. *
***************************************************************************

DiskTimer II is a very simple test.  It obtains the read (write) time
by repeatedly reading (writing) the same area of the disk.  It obtains
the seek time by alternately reading two sectors separated by some
fixed distance on the disk. 

The big problem with these tests is that DiskTimer's trivially and
grossly deceived by caching.  The control panel cache isn't the
problem, since that applies to the file system, and DiskTimer II calls
the driver directly.  But, any cache implemented by the driver or
controller makes DiskTimer's results nearly meaningless.  

So, a DiskTimer II seek time of "0" means that the driver or
controller is caching the two sectors involved in the seek test. 

BTW, it looks like your HD 20 SC would benefit from formatting with a
tighter interleave.  Was it originally formatted on the IIci, or on a
slower machine? 
--
Ephraim Vishniac    ephraim@think.com   ThinkingCorp@applelink.apple.com
 Thinking Machines Corporation / 245 First Street / Cambridge, MA 02142
        One of the flaws in the anarchic bopper society was
        the ease with which such crazed rumors could spread.