Re: Disk sizes and performance

Well, I was goiung to point you to a couple of itemsin the IBM Knowledge
Base.
They USED to be public documents, now they're "secured".  If you have a
support line contract go searching for these:

IBM AS/400 Support Line Technical Document
Document Number: 15135640
____________________________________________________________
Functional Area:
                Operating System
Subfunctional Area:
                Performance
Sub-Subfunctional Area:
                System Performance

____________________________________________________________
Product:
           Performance Tools - AS/400 PT B (5769PT1B1)
           Performance Tools - PERF TLS BEST1 (5716PT1B1)
           Performance Tools - PERF TLS CAPACTY PLN (5763PT1B1)


Release:
           ALL

____________________________________________________________

Document Title: AS/400 Disk Arm Requirements

Document Description:

This document contains information available only to customers who have
purchased a Support Line
contract and who have completed the online registration.

    I have a Support Line contract, and I am a Registered user.

    I have a Support Line contract, and I would like to Register.

For more information about Support Line services, refer to the following
Web site:

http://www.as.ibm.com/asus/swsupport.html

IBM AS/400 Support Line Technical Document
Document Number: 12402126
____________________________________________________________
Functional Area:
                Operating System
Subfunctional Area:
                Performance
Sub-Subfunctional Area:
                General

____________________________________________________________
Product:
           OS/400 WORK MGMT (5716SS1WM)
           OS/400 WORK MGMT (5763SS1WM)
           OS/400 WORK MGMT (5769SS1WM)


Release:
           ALL

____________________________________________________________

Document Title: Arm Count Table for AS/400 Models

Document Description:

This document contains information available only to customers who have
purchased a Support Line
contract and who have completed the online registration.







"Robin Sapiro" <robin.sapiro@home.com> on 99-08-01 20:34:25

Please respond to MIDRANGE-L@midrange.com

To:   MIDRANGE-L@midrange.com
cc:    (bcc: Neil Palmer/Dpslink)

Subject:  Disk sizes and performance




I am looking for some ball park estimates on when to use a greater number
of
small disk drives versus a smaller number of larger disk drives.
Conventional wisdom is that the more disk arms you have the better the
performance. Obviously this is directly related to the amount of I/O being
done on the system. I feel however that there is some point (total disk
required) at which adding additional disk arms does not have any
significant
improvement on performance and at that point it is more beneficial to use
larger disks which results in financial savings in the form or lesss $/GB,
less controllers, less racks etc.
Any opinions as to what the magic number might be. ie if less than n GB on
a
system, use 4 GB drives. for n-m GB on a system use 8.5 GB drives and for
greater than m GB on a system use 17 GB drives.
Also what is the general opinion as to the DASD % utilisation at which I/O
performance begins to degrade.






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