Compaq ProLiant 1000 I/O Performance Tuning of Compaq Servers - Page 16

I/O Performance Tuning of Compaq Servers

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ECG044.0399

service. To a client, distributing the workload means that any individual request will be filled

more quickly. By spanning the data and workload to multiple devices, it becomes more likely that

an individual drive will be able to handle a request immediately. In effect, RAID allows parallel

retrieval of data. With RAID more requests can be filled simultaneously than with a single drive.

Perhaps the greatest benefit that can be gained from using RAID technology is data guarding.

RAID systems can provide highly reliable redundancy for storage systems. In some cases RAID

can even reconstruct data that is on a drive that has failed. Proper implementation of RAID,

however, requires a basic knowledge of the systems and options involved.

RAID 0

(

No Fault Tolerance):

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. You may consider assigning RAID level 0 to drives that require large capacity (in some

cases, full capacity of the disks) and high speed, and can afford the loss of data in the event of a

disk failure.

RAID 1

(

Disk Mirroring):

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 provides high level of fault tolerance, 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 4

(Data Guarding):

In RAID 4 one of the disks in the stripe set is used for drive parity. To

calculate the parity, data from all the data drives in the stripe set are read. RAID 4 is not

commonly used for database applications.

Data

Data

Data

Data

1

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4

Data

Data

Data

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Data

Data

Data

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Data

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RAID 0 - Data Striping

Data

Data

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Data

Data

Data

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Data

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Parity

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RAID 4 - Data Guarding

Data

2

Data

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Data

1

Copy

of

Data

1

Data

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Parity

1

Copy

of

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RAID 1 - Drive Mirroring

Data

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Parity

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Parity

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Parity

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RAID 5 - Distributed Data Guarding

Figure 5.

Data and Parity Distribution for RAID

Compaq ProLiant 1000 I/O Performance Tuning of Compaq Servers - Page 16

Raid 0, Raid 1, Raid 4

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