Compaq 108164-003 - ProLiant - 800 White Paper page 19

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(cont.)
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Lastly, our one controller testing shows that once we added another four drives to our test
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environment (8 to 12 drives), the increase in performance was 25%, as shown in Figure 8.
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Summary of Findings – Like Drive Scaling
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Doubling the number of drives in our system, in either a RAID 0 or 5 environment,
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increased performance by more than 50% when using 2 or 4GB drives. Also, by adding
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four more drives to our environment (making a total of 12 drives) as shown in Figure 8, we
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learned that our performance gain increased another 25%. However, keep in mind that
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by doubling our drives in our test environment we improved performance, but we also
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doubled the drive cost for this configuration. If performance is a concern, this is an
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effective solution for your environment.
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To help assist you in deciding what is right for your environment, Table 8 lists some
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advantages and disadvantages of like drive scaling.
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Like Drive Scaling Advantages and Disadvantages
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Advantages
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Eliminates bottlenecks because you
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minimize seek time.
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Increases I/O concurrency because you
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have more drives processing disk requests.
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Increases cumulative transfer rate because
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the more drives you add to your system the
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more data can be transferred.
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Idle time on the controller decreases
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because cumulative disk performance
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increases.
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L C
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I K E AP AC I T Y
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Like capacity scaling, unlike like drive scaling, is when you use similar or "like" drives and
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scale them to determine if your environment needs multiple lower capacity drives or fewer
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larger capacity drives. For example, if you need four Gigabytes of disk storage, what
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should you purchase to meet your capacity requirements and provide the best system
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performance? Should you buy one 4.3-Gigabyte drive or two 2.1-Gigabyte drives? If you
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currently have hard drives in your environment that are not using the total storage
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capacity of the disk, using like drives with a smaller capacity might be the right solution
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for you.
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Table 8:
Disadvantages
Drive cost increases each time you add more drives.
Using smaller size drives limits your maximum capacity per
controller. For example, the Compaq SMART-2 Array Controller
supports up to 14 drives. By using fourteen 2GB drives, your data
capacity equals 28GB. By using fourteen 4GB drives, your data
increases to 56GB.
By adding more drives to your system you have more disks to
manage, thus increasing the probability of disk failure.
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C AL AB I L I T Y