Compaq 108164-003 - ProLiant - 800 White Paper page 29

ECG025.0997
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HITE APER
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Redundant Arrays of Inexpensive Disks Levels
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RAID Level
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RAID 0 (No Fault Tolerance)
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RAID 1 (Disk Mirroring)
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. . RAID 5 (Distributed Data Guarding)
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D S
I S K U B S Y S T E M
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Within this document we have learned how a few key disk performance concepts can help
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you identify bottlenecks and improve performance within your disk subsystem. We have
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gathered these concepts and summarized the information. These concepts are:
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Disk-Related Measurement Terms
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Understanding the Transfer Rates within the Disk Subsystem
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The Importance of File System Cache
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Benefits of Scaling
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Table 13:
Description
This RAID level is not a true fault tolerance method because it does
not provide data redundancy; therefore, provides no fault protection
against data loss. RAID 0 is known as "stripe sets" because data
is simply striped across all of the drives in the array. This
configuration provides high performance at a low cost, however, you
incur a risk of possible data loss.
This configuration of mirrored sets of data uses 50 percent of drive
storage capacity to provide greater data reliability by storing a
duplicate of all user data on a separate disk drive. Therefore, half of
the drives in the array are duplicated or "mirrored" by the other half.
This RAID level does provide performance equal to or better than
RAID 0, but your drive cost doubles because this level requires
twice as many disk drives to store the same amount of data and
therefore might not be cost-effective for your environment.
RAID 5 is commonly called "Distributed Data Guarding" or "Stripe
Sets with Parity". This level of RAID actually breaks data up into
blocks, calculates parity, then writes the data blocks in "stripes" to
the disk drives, saving one stripe on each drive for the parity data.
This method is cost effective with the added benefit of high
performance because the parity information is distributed across all
the drives. The total amount of disk space used for redundancy is
equivalent to the capacity of a single drive; therefore, the overall
cost for this method of fault tolerance is lower than Disk Mirroring
(RAID 1).
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U M M AR Y O F I N D I N G S