Vectronix 2/VECTRONIX2.iso/FILES_07/ICDP655A.ZIP/DOCS/ENGLISH/RATEHD.DOC

Text File | 1994-06-03 | 8KB | 182 lines

RATEHD.PRG & RATEHD.DOC
Copyright 1989-1991  ICD, Inc.

This document and the program RATEHD.PRG, may be distributed by
any non-commercial means (may not be sold) as long as the they
are distributed together and no modifications are made.
Language translations are allowed.

The copyright holder is:

     ICD, Inc.
     1220 Rock Street
     Rockford, IL  61101-1437

     Voice:  [phone]
     BBS:    [phone]
     FAX:    [phone]

RATEHD.PRG was written in Personal Pascal, a product of ICD, Inc.
-----------------------------------------------------------------

RATEHD was written to show performance characteristics of
various hard disk drives.  It was developed at ICD to allow fair
comparison when evaluating hard disk drive mechanisms, embedded
SCSI drives and SCSI controllers when used on the Atari ST.  It
does not go through a hard disk handler (like ICDBOOT.SYS) so it
is not useful in rating the speed of different handlers.
Generally, the ICD hard disk handler provides a significant
speed improvement in actual use due to its caching.

We were a bit apprehensive about releasing this to the public
because of our fears that people would not understand it and
will use it for the wrong purpose.  It is intended as a
comparison test and should not be used to verify a drive or
controller against printed specifications.  Drive manufacturers
test their drives on specialized test equipment and not on an
Atari ST.  Data rates are also usually shown as a burst rate.
What we are measuring is the sustained rate, which is closer to
the top end in real life usage.

Our final decision to release RATEHD was twofold:

1) There is too much misinformation out there when it comes to
   computers and hard drives.  There needed to be a uniform
   benchmark test for the Atari ST.  Magazine reviews have
   typically mislead the public, not maliciously, but because of
   the reviewer's ignorance on the subject and lack of
   scientific testing methods.  Now you have a benchmark; just
   don't abuse it.

2) When we finished the FA-ST Tape Backup, we realized that a
   hard drive system would need a certain amount of finesse to
   keep up with the streaming tape.  If the tape had to keep
   backing up and waiting for the hard drive to catch up, the
   backup time would become laboriously long and almost not
   usable.  A data rate of about 300 K/s (kilobytes per second)
   is required to keep the tape moving without any stopping and
   backing up.  As the data rate gets slower, the tape will begin
   to backup and restart several times per partition.  A data
   rate of less than 200 K/s would probably become unbearable at
   attempting a backup.

We have tested many drives and controllers at their optimum
interleaves and found that Adaptec MFM controllers (including
Atari SH204, Megafile 20) run about 300 K/s if they are formatted
at 1:1 interleave.  Adaptec RLL controllers (including Atari
Megafile 30 and 60) run about 315 K/s at 2:1 interleave.  Omti
MFM controllers move along about 360 K/s using 1:1 with Omti RLL
at about 375 K/s at 1:1.  Embedded controller drives are usually
the speedsters with the Seagate ST138N and ST157N cruising at 550
K/s at 1:1.  The quickest we have measured was a Quantum LP105S
which flies at 1197 K/s which is probably fast enough to do real
time video.  It also had 21 ms average access time and had a 105
Megabyte formatted capacity.


THE PROBLEM WITH MOST TEST METHODS
----------------------------------

There are many variables in something as complex as a computer
with a hard disk drive that can make testing a cumbersome task.
The most obvious way to test hard drive speed is to copy files
from a hard drive to a RAMDISK and then back to a clean hard
drive while timing the process.  Although on the surface a test
like this appears sufficient, it cannot give an accurate picture
of what to expect in performance after using the drive for a
while.  Both hard drives would need to be freshly formatted (no
files yet) and with identical partition sizes.  If not freshly
formatted, the DOS fat table delays and fragmentation would enter
a significant amount of error into the rating equation.  Of
course the same DOS and same computer must also be used.

While this seems like a reasonable test method, it would only
show the data rate (assuming both drives were formatted at their
optimal interleave).  Step rate in this type of test would not be
a measurable factor as it would later on when the files on the
drives become fragmented.  Fragmentation occurs as a hard drive
gets used and files are modified.  They increase in size and
when rewritten to the drive, not all the file parts are in
consecutive sectors anymore, probably not even in the same area
of the disk.  The file eventually becomes a group of "fragments."
This is where the movement of the head from track to track (step
rate measured as average access time) really becomes an
important speed factor.  It would not be an easy task to create
two freshly formatted drives of different manufacture with
identical fragmentation on each drive.

Many of the magazine reviews we have seen give no indication of
the test method.  It is almost as if the numbers were arrived at
by magic.  We now offer RATEHD as a solution to all magazine
reviewers desiring to test hard disk drives.  If you all use
this, then the results can be believable.

Since RATEHD does not use the OS nor the hard disk handler, it
is easily repeatable and virtually foolproof.  Both are important
factors in any test method.  It will run on any hard drive and
does not care about how the partitions are set up nor does it
matter what the file structure is like.  Since RATEHD *never*
writes to the disk, it is totally safe and can be run at any
time.


ABOUT THE PROGRAM
-----------------

RATEHD begins at SCSI ID #0, Logical Unit Number 0, and proceeds
to check LUNs 0-3 for each SCSI ID going through all SCSI IDs 0-7
except special cases for ID #6 (reserved for our real time clock)
and ID# 7 (where it only reads LUN 0).  When the program finds a
hard drive present, it will print the manufacturers
identification under Device Name, and proceed with the tests.
After each drive is tested, it will display the results and
search for the next drive.  When finished with all drives, RATEHD
will allow you to RETEST or EXIT back to the desktop.  (A screen
dump will print the results.)

Don't worry: It is only a read test so no damage will be done to
your drive data.


ABOUT THE TESTS
---------------

The Data Rate Test
     In this test, one megabyte of data is read (2,000 sectors)
     in 100 sector continuous blocks (burst mode).  This is timed
     and the math is done to calculate the number of K/s
     (Kilobytes read in one second).

The Average Access Test
     The Average Access is based on an assumed 16 megabyte
     partition beginning with sector 0 and ending with sector
     31,000.  The head is told to read a sector at the innermost
     cylinder of the partition area (31,000) then to read one in
     the outermost cylinder (0).  This is repeated 50 times but
     each time the sector number is adjusted so that the head
     will move 1/50 less distance. If there were 51 tries, the
     head would end up on the center cylinder of the partition
     (15,500), not stepping at all for the inner and outer
     cylinders.

     This movement is timed and the sector read time is removed.
     An average time for the head travel is then calculated and
     shown in ms (milliseconds).  Since this average time also
     includes the command overhead time, it will be slightly
     higher than specifications from the drive manufacturer.


WHAT YOU HAVE LEARNED
---------------------

There are really only two significant variables concerning
performance with a hard disk.  These are Data Rate and Average
Access.  We are assuming that you are concerned about speed and
have the optimum interleave on your drive.

There is one other bottleneck that does affect hard disk
performance.  The Disk Operating System is a major slowdown.  To
optimize your DOS speed get TOS 1.4 from Atari as soon as you
can.  Using it, we have seen a tremendous improvement in both
speed and reliability.  Thank you Atari!