IBM SG24-4576-00 manual Summary of RAID Performance Characteristics

1.6.6.8 Summary of RAID Performance Characteristics

RAID-0:Block Interleave Data Striping without parity

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Fastest data-rate performance

Allows seek and drive latency to be performed in parallel Significantly outperforms single large disk

RAID-1:Disk Mirroring/Disk Duplexing and Data Strip mirroring (RAID-1, Enhanced)

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Fast and reliable, but requires 100% disk space overhead Data copied to each set of drives

No performance degradation with a single disk failure

RAID-1 enhanced provides mirroring with an odd number of drives

RAID-2:Bit Interleave Data Striping with Hamming Code

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Very fast for sequential applications, such as graphics modelling Almost never used with PC-based systems

RAID-3:Bit Interleave Data Striping with Parity

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Access to all drives to retrieve one record Best for large sequential reads

Very poor for random transactions Poor for any write operations

Faster than a single drive, but much slower than RAID-0 or RAID-1 in random environments

RAID-4:Block Interleave Data Striping with one Parity Disk

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Best for large sequential I/O Very poor write performance

Faster than a single drive, but usually much slower than RAID-0 or RAID-1

RAID-5:Block Interleave Data Striping with Skewed Parity

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Best for random transactions

Poor for large sequential reads if request is larger than block size Better write performance than RAID-3 and RAID-4

Block size is key to performance, must be larger than typical request size Performance degrades in recovery mode (when a single drive has failed)

Table 7. Summary of RAID Performance Characteristics

RAID Level	Capacity	Large Transfers	High I/O Rate	Data Availability
Single Disk	Fixed (100%)	Good	Good	￿1￿
RAID-0	Excellent	Very Good	Very Good	Poor ￿2￿
RAID-1	Moderate (50%)	Good	Good	Good
RAID-2	Very Good	Good	Poor	Good
RAID-3	Very Good	Very Good	Poor	Good
RAID-4	Very Good	Very Good	Poor	Good
RAID-5	Very Good	Very Good	Good	Good

Note:

￿1￿The MTBF (mean time before failure) for single disks can range from 10,000 to 1,000,000 hours. ￿2￿Availability = MTBF of one disk divided by the number of disks in the array.

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