2013Sp-CS61C-L38-dg-IO-Disks

Assume have 4 disks of data for this example

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Unformatted text preview: 6X Array Reliability •  Reliability - whether or not a component has failed –  measured as Mean Time To Failure (MTTF) •  Reliability of N disks = Reliability of 1 Disk ÷ N (assuming failures independent) –  50,000 Hours ÷ 70 disks = 700 hour •  Disk system MTTF: Drops from 6 years to 1 month! •  Disk arrays too unreliable to be useful! Redundant Arrays of (Inexpensive) Disks •  Files are “striped” across mulWple disks •  Redundancy yields high data availability –  Availability: service sWll provided to user, even if some components failed •  Disks will sWll fail •  Contents reconstructed from data redundantly stored in the array ⇒ Capacity penalty to store redundant info ⇒ Bandwidth penalty to update redundant info RAID : Redundant Array of Inexpensive Disks •  Invented @ Berkeley (1989) •  A mulW- billion industry 80% non- PC disks sold in RAIDs •  Idea: –  Files are “striped” across mulWple disks –  Redundancy yields high data availability •  Disks will sWll fail –  Contents reconstructed from data redundantly stored in the array •  ⇒ Capacity penalty to store redundant info •  ⇒ Bandwidth penalty to update redundant info “RAID 0”: No redundancy = “AID” •  Assume have 4 disks of da...
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