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Performance Considerations for Tape Drives and Libraries 11

RAID 5

With a RAID 5 array, data is striped across the disk array at the byte level and error correction data,

or parity data, is also striped across the disk array. RAID 5 arrays tend to have very good random

read performance; this read performance generally improves as the number of disks in the array

increases. With the larger disk arrays, read performance can actually outperform RAID 0 arrays

because the data is distributed over an additional drive. In additional, parity information is not

required during normal reads.

Restores from tape to a RAID 5 array tend to be nominal because it involves additional overhead

for calculating and writing the parity information.

Figure 1-4. Example RAID 5 Configuration

D10

D13

D11

D14

D12

D15

D16

SCSI or RAID

Controller

Tape Drive

Read/Write

D = Data Byte

Hard Drive 1 Hard Drive 2 Hard Drive 3 Hard Drive 4

P = Parity Byte

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 175 176

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Dell PowerVault TL2000 Manual do Utilizador Página 11