Dell PERC 4/DC User Manual download pdf (Page 24)

Table 4-7.PhysicalDrivesRequiredforEachRAIDLevel

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Summary of RAID Levels

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RAID 0 uses striping to provide high data throughput, especially for large files in an environment that does not require fault tolerance.

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RAID 1 uses mirroring and is good for small databases or other applications that require small capacity, but complete data redundancy.

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RAID 5 provides high data throughput, especially for small random access. Use this level for any application that requires high read request rates, but low

write request rates, such as transaction processing applications. Write performance is significantly lower for RAID 5 than for RAID 0 and RAID 1.

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RAID 10 consists of striped data across mirrored spans. It provides high data throughput and complete data redundancy, but uses a larger number of spans.

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RAID 50 uses parity and disk striping and works best with data that requires high reliability, high request rates, high data transfers, and medium-to-large

capacity. Write performance is limited to the same as RAID 5.



Storage in an Array with Drives of Different Sizes

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For RAID levels 0 and 5, data is striped across the disks. If the hard drives in an array are not the same size, data is striped across all the drives until one or

more of the drives is full. After one or more drives are full, disk space left on the other disks cannot be used. Data cannot be written to that disk space

because other drives do not have corresponding disk space available.

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Figure4-1 shows an example of storage allocation in a RAID 5 array. The data is striped, with parity, across the three drives until the smallest drive is full. The

remaining storage space in the other hard drives cannot be used because not all of the drives have disk space for redundant data.

Figure 4-1. Storage in a RAID 5 Array

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Storage in RAID 10 and RAID 50 Arrays

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You can span RAID 1 and 5 arrays to create RAID 10 and RAID 50 arrays, respectively. For RAID levels 10 and 50, you can have some arrays with more storage

space than others. After the storage space in the smaller arrays is full, you can use the additional space in larger arrays can store data.

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RAID Level

Minimum # of Physical Drives

Maximum # of Physical Drives for PERC 4/SC

Maximum # of Physical Drives for PERC 4/DC and 4e/DC

0

1

14

28

1

2

5

3

14

28

10

4

14

28

50

6

14

28

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Dell PERC 4/DC User Manual Page 24

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