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RAID CS5493/7493

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RAID : What is it? Redundant Array of Independent Disks configured into a single logical storage unit.

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RAID : Implemented with current disk storage technologies: SATA Serial Advanced Technology Attachment SCSI Small Computer System Interface SSD Solid State Disk

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Storage Performance Factors

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Capacity

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Storage Performance Factors Capacity Noise Level

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Storage Performance Factors Capacity Noise Level Power Consumption

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Storage Performance Factors Capacity Noise Level Power Consumption Data Transfer Rate

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Storage Performance Factors Capacity Noise Level Power Consumption Data Transfer Rate Reliability

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Storage Performance Factors Capacity Noise Level Power Consumption Data Transfer Rate Reliability Temperature

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Performance Pyramid Fast Cheap Good S-S, Steady State

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Performance Pyramid Fast Faster IO transfer rate Cheap Lower cost per GB Good more reliable, lower temp, less noise Less power consumption

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Performance Pyramid FastCheap S-S Good

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Technology Comparison Single Unit Storage Devices $/GBMTBFIO RateNoisePower SATA-HDD~$0.05< 90 K-hrs< 100 MB/s~40dB2.5-10W SASCSI-HDD~$1.00~ 90 K-hrs~ 100 MB/s~50dB10W SATA-SSD~$0.50~ 90 K-hrs~ 500 MB/s> 0 dB< 2.5W

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RAID Purpose RAID can improve Reliability (except level-0) Data Transfer Rates through parallelism (faster than the single unit rates)

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RAID Purpose RAID can improve Reliability Data Transfer Rates RAID sacrifice Cost per GB increases

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Common RAID Levels RAID-0 RAID-1 RAID-3 RAID-5 RAID-6 RAID-1+0 RAID-0+1

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RAID-0 Striped, no mirror, no parity IO Speedup bounded by number of drives and Amdahls Law. No fault tolerance Minimum of 2 drives

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RAID-1 No Striping, no parity, uses a mirror 2 drives (data and mirror) Fault tolerance is one

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RAID-3 Byte level striping and Dedicated parity drive Parity uses the logical exclusive-or operation n-1 IO speed-up limit Minimum of 3 drives required. Fault tolerance is one

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RAID-5 Block level striping Distributed parity Parallel IO data transfer across the array Minimum of 3 drives required Fault tolerance is one

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RAID-6 Block level striping Distributed and redundant parity Parallel IO data transfer across the array. Minimum of 4 drives required Fault tolerance is two

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RAID-1+0 Combination of RAID-1 and RAID-0 Logical drives are physical pairs configured as RAID-1 devices The logical drives are then configured as a stripe. Fault tolerance is 1.

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RAID-0+1 Combination of RAID-1 and RAID-0 A stripe of drives is mirrored Fault tolerance is 1.

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Relative Reliability of RAID Class exercise