Compaq 108164-003 - ProLiant - 800 White Paper page 18

A discussion of RAID levels used
in this white paper can be found
in the "Preventing Data Loss
While Maintaining Performance"
section of this document.
ECG025.0997
W P
HITE APER
(cont.)
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growth and increasing capacity requirements. For instance, choose the correct server
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configuration for your environment, yet leave slots available for future disk controllers that
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might be necessary to support future capacity requirements.
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Like Drive Scaling
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Like drive scaling is defined as comparing similar drives with the same RAID level and
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"scaling" or adding more drives to your system so that you can measure cumulative disk
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performance. Drive scaling can be summarized as the more drives you add to your
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system, the better the performance. However, the question you need to ask yourself is
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"When does the cost of adding more drives out weigh the performance gain?".
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To answer this question, Compaq tested controllers using the same RAID configuration
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and added drives, then measured the system performance effects. Let's now view those
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results and understand the effects of drive scaling.
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. . Like Drive Scalability Test Results
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Our one controller testing, illustrated in Figure 8, revealed that when using 2GB drives
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. . configured in a RAID 0 environment approximately a 50% performance increase was
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achieved when the drives were doubled. For example, we doubled the number of drives
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in the test configuration environment from 4 to 8 and experienced a 57% increase
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in performance.
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20,000,000.00
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18,000,000.00
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16,000,000.00
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14,000,000.00
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12,000,000.00
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10,000,000.00
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8,000,000.00
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6,000,000.00
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4,000,000.00
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2,000,000.00
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-
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4
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Figure 8: Like Drive Scaling in a RAID 0 Environment.
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In addition, we found when using 2GB drives in a RAID 5 configuration (4+1 vs. 8+1
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drives), performance also increases over 50%. A performance increase was also
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obtained when using 4GB drives on one controller in either a RAID 0 or 5 environment.
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18
Like Drive Scaling (RAID 0 - 1 Controller)
57%
8 16 20 24 28
Number of Clients
25%
96%
32 36 40 44 48
12 x 2GB
8 x 2GB
4 x 2GB
52 56 57