Compaq 108164-003 - ProLiant - 800 White Paper page 23

ECG025.0997
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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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Figure 12: Like Capacity Scaling in a RAID 5 Environment.
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Table 9 lists the advantages and disadvantages of like capacity scaling. Review and
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consider these items before making any decisions on what is right for your environment.
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Like Capacity Scaling Advantages and Disadvantages
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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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Higher number of drives, improves the
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performance (more concurrency).
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23
Like Capacity Scaling (RAID 5 - 1 Controller)
16 20 24 28 32
Number of Clients
Table 9:
Disadvantages
Purchasing more disks for the same amount of disk space could be
viewed as a more expensive solution for your environment. For
example, purchasing four 2GB drives instead of two 4GB drives.
By not buying the latest technology, you might be missing new
features that increase performance. For example, the latency time
for a new 9GB disk might be faster than an older 4GB disk.
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
increase to 56GB.
By adding more drives to your system you have more disks to
manage, thus increasing the probably of disk failure.
11+1 x 2GB
5+1 x 4GB
2+1 x 9GB
28%
36 40 44 48 52 56 57