Jim,

     My own experience coming from a mixed environment of (17) Eagle and (10)
     Coyote drives on a HP960 to my current environment of a KS959/300 with (36)
     2GB F/W SCSI drives has given me the following insights:

     1.  The new drives are much faster.  My guess is at least a factor of 3 and
         possibly 4 times the sustained IO speed of the old drives.

     2.  Using drives of the same size and speed characteristics makes a system
         behave much more smoothly than a mixed disk environment.  Since MPE
         tries to keep each disk, except for LDEV 1,  at a similar percentage of
         fullness, the 4GB drive would get at least twice the amount of data
         than the 2GB drive.  Also, if the 2GB drive is LDEV1, the 4GB drive
         would probably get even more placed on it by MPE.

     Therefore, I recommend that you consider buying either three 2GB drives
     (*My preference*) or two 4GB drives instead of the two dissimilar drives
     that you are contemplating now.  I think that you'll find the overall
     apparent performance will be much better than mixing disk geometries.  I
     also recommend that you put your disks on their own channel to keep
     everything running at top speed.

     My two cents' worth.  As always, YMMV!

     - John Hornberger
       Sr. Systems Programmer
       General Signal Services

______________________________ Reply Separator _________________________________
Subject: Disk Utilization
Author:  Therm-O-Link <[log in to unmask]> at Internet2
Date:    2/27/97 1:55 PM


Here's our current disk layout:

4 2203A 670MB drives, SYSGEN paths: 4.1.0, 4.1.1, 4.5.2, 4.1.2
2 7937H 571MB drives, SYSGEN paths: 4.1.4, 4.1.5

Roughly 3.8 GB, all in the <long_name> volume set on a Series 948.

We are contemplating (very seriously) going to a series 918 with two
disk drives, a 2GB and a 4GB.  We have a 40-user license and do not
exceed 32 sessions at any time.  We will probably (over the next year
or two) add another 20 sessions, but the total session count will not
exceed 64.  We have most of our users accessing one application, with
two or three others accessing a second application.

My nebulous-question-of-the-week is:

Will we see any disk access time degradation by going from six spindles
down to two or will the newer drives be quicker?

If the answer to this is the infamous "It depends", how can I determine
for sure what the answer will be for us?  Thanks in advance.

Jim Phillips                            Manager of Information Systems
E-Mail: [log in to unmask]      Therm-O-Link, Inc.
Phone: (330) 527-2124                   P. O. Box 285
  Fax: (330) 527-2123                   Garrettsville, Ohio  44231