Compaq 108164-003 - ProLiant - 800 White Paper page 20

ECG025.0997
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HITE APER
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Like Capacity Scaling
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Since like capacity scaling can affect your system, it is important to understand the impact
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it might have on system performance. To be able to determine this information, we tested
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like capacity scalability by maintaining the same total disk capacity for each test (8GB or
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24GB) and added different quantities of drives to a single disk controller. The results of
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. . these tests determine if system performance improves when using multiple lower capacity
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drives or fewer larger capacity drives. In the next few sections of this white paper we
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analyze these different configurations.
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Like Capacity Test Results
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Earlier we discussed concurrency and how the more spindles (disks) you have in your
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system the better the performance would be because more I/O requests are being
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concurrently processed. Overall our single disk controller like capacity tests provide
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evidence that support our theory on concurrency. For example, if you need 8 Gigabytes
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of storage capacity, our test show the benefits of using four 2GB disks instead of two 4GB
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disks. The storage capacity is the same; however, the performance increase is 68% as
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shown in Figure 9. We needed only one 9GB drive in our test to reach the eight Gigabyte
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storage capacity requirement, so consequently concurrency could not take place and is
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therefore not beneficial in this configuration.
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16,000,000
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14,000,000
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12,000,000
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10,000,000
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8,000,000
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6,000,000
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4,000,000
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2,000,000
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0
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4 8
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Figure 9: Like Capacity Scaling in a RAID 0 Environment.
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20
Like Capacity Scaling (RAID 0 - 1 Controller)
68%
16 20 24 28 32
Number of Clients
4 x 2GB
2 x 4GB
1 x 9GB
36 40 44 48 52 56 57