Compaq 108164-003 - ProLiant - 800 White Paper page 24

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Summary of Findings – Like Capacity Scaling
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Our test results conclude that by doubling the number of drives in a system, regardless of
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the data storage capacity requirements and the fault tolerance used, we consistently
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received an improvement in performance. However, the performance increase lessened
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as we added more and more drives to our system. We should also consider the
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limitations of each configuration. For example, by using lower capacity drives on one
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controller you improve performance, however, you sacrifice using the maximum disk
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capacity on that controller.
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To decide which test configuration best fits your needs, we recommend that you first
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review your system requirements, weigh the advantages and disadvantages of like
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capacity scaling, then purchase the correct drive capacity along with the correct
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number spindles for your environment. Refer to the "Performance Measurement Tools"
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section within this document for information on tools that can assist you in measuring
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system performance.
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D C
I S K O N T R O L L E R
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When analyzing controller scalability, the focus is on the performance difference between
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a single controller using a specified number of spindles versus multiple controllers using
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equally divided drives. Does one controller with all drives attached to it out perform two
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controllers with the drives divided equally among the controllers? For example, let's say
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you configure fourteen disk drives in one controller, then split the fourteen drives (seven
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on each controller) and configure them in a two-controller environment. Which one out
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performs the other? Disk controller scaling will answer this question for us.
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Disk Controller Scaling
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The key to disk controller scaling is to find the point at which your hardware does not
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produce a significant benefit in system performance. We define this point by testing the
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scalability of a controller. To scale a controller, we used a constant number of drives with
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equal disk capacity and tested a single controller versus multiple controllers. For
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example, the testing results determine if two SMART-2 Controllers with a fewer number of
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drives on each controller provide better performance than one SMART-2 Controller
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configured with all the drives.
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