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Berkeley COMPSCI 61C - Redundant Arrays of Inexpensive Disks

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Slide 1Slide 2AgendaAgendaEvolution of the Disk DriveArrays of Small DisksSlide 7RAID: Redundant Arrays of (Inexpensive) DisksSlide 9Redundant Array of Inexpensive Disks RAID 3: Parity DiskSlide 11Inspiration for RAID 5RAID 5: High I/O Rate Interleaved ParityProblems of Disk Arrays: Small WritesTech Report Read ‘Round the World (December 1987)RAID-IRAID IIRAID IIRAID SummaryAgendaAdministriviaSome Survey ResultsSome Survey ResultsSome Survey ResultsSome Survey ResultsSome Survey ResultsAgendaCS61c is NOT really about C ProgrammingOld School View of Software-Hardware InterfaceNew-School Machine Structures (It’s a bit more complicated!)6 Great Ideas in Computer ArchitectureLevels of Representation/InterpretationMoore’s LawTypical Memory HierarchyMemory HierarchyParallelismForms of ParallelismPerformance ImprovementGreat Idea #6: Dependability via RedundancyRandy’s Course SummaryAgendaWhat to Emphasize about Cal culture?Cal Cultural History: Football!ABCs of American FootballFootball FieldSpectacle of American FootballSpectacle of American Football1982 Big Game: “The Play”Notes About “The Play” (1/2)Notes About “The Play” (1/2)Slide 51The Future for Future Cal AlumniNotes About “The Play”CS 61C: Great Ideas in Computer Architecture (Machine Structures)Redundant Arrays of Inexpensive DisksInstructors:Randy H. KatzDavid A. Pattersonhttp://inst.eecs.Berkeley.edu/~cs61c/fa101Spring 2011 -- Lecture #2701/14/201901/14/2019 Spring 2011 -- Lecture #27 2Agenda•RAID•Administrivia•Course Summary (Randy)•Cal Culture (Dave)•Course Evaluation01/14/2019 Spring 2011 -- Lecture #27 3Agenda•RAID•Administrivia•Course Summary (Randy)•Cal Culture (Dave)•Course Evaluation01/14/2019 Spring 2011 -- Lecture #27 4Evolution of the Disk Drive01/14/2019 Spring 2011 -- Lecture #27 5IBM RAMAC 305, 1956IBM 3390K, 1986Apple SCSI, 1986Can smaller disks be used to close gap in performance between disks and CPUs?Arrays of Small Disks01/14/2019 Spring 2011 -- Lecture #27 614”10”5.25”3.5”3.5”Disk Array: 1 disk designConventional: 4 disk designsLow EndHigh EndReplace Small Number of Large Disks with Large Number of Small Disks! (1988 Disks)01/14/2019 Spring 2011 -- Lecture #27 7Capacity Volume PowerData Rate I/O Rate MTTF CostIBM 3390K20 GBytes97 cu. ft.3 KW15 MB/s600 I/Os/s250 KHrs$250KIBM 3.5" 0061320 MBytes0.1 cu. ft.11 W1.5 MB/s55 I/Os/s50 KHrs$2Kx7023 GBytes11 cu. ft.1 KW120 MB/s3900 IOs/s??? Hrs$150KDisk Arrays have potential for large data and I/O rates, high MB per cu. ft., high MB per KW, but what about reliability?9X3X8X6XRAID: Redundant Arrays of (Inexpensive) Disks•Files are "striped" across multiple disks•Redundancy yields high data availability–Availability: service still provided to user, even if some components failed•Disks will still fail•Contents reconstructed from data redundantly stored in the array Capacity penalty to store redundant info Bandwidth penalty to update redundant info01/14/2019 Spring 2011 -- Lecture #27 8Redundant Arrays of Inexpensive DisksRAID 1: Disk Mirroring/Shadowing01/14/2019 Spring 2011 -- Lecture #27 9•Each disk is fully duplicated onto its “mirror” Very high availability can be achieved• Bandwidth sacrifice on write: Logical write = two physical writesReads may be optimized• Most expensive solution: 100% capacity overheadrecoverygroupRedundant Array of Inexpensive Disks RAID 3: Parity Disk01/14/2019 Spring 2011 -- Lecture #27 10P100100111100110110010011. . .logical record10100011110011011010001111001101P contains sum ofother disks per stripe mod 2 (“parity”)If disk fails, subtract P from sum of other disks to find missing informationStriped physicalrecordsRedundant Arrays of Inexpensive Disks RAID 4: High I/O Rate ParityD0 D1 D2D3PD4 D5 D6PD7D8 D9PD10D11D12PD13D14D15PD16 D17D18D19D20 D21 D22D23P...............Disk ColumnsIncreasingLogicalDiskAddressStripeInsides of 5 disksInsides of 5 disksExample: small read D0 & D5, large write D12-D15Example: small read D0 & D5, large write D12-D1501/14/2019 11Spring 2011 -- Lecture #27Inspiration for RAID 5•RAID 4 works well for small reads•Small writes (write to one disk): –Option 1: read other data disks, create new sum and write to Parity Disk–Option 2: since P has old sum, compare old data to new data, add the difference to P•Small writes are limited by Parity Disk: Write to D0, D5 both also write to P disk 01/14/2019 Spring 2011 -- Lecture #27 12D0 D1 D2D3PD4 D5 D6PD7RAID 5: High I/O Rate Interleaved Parity01/14/2019 Spring 2011 -- Lecture #27 13Independent writespossible because ofinterleaved parityIndependent writespossible because ofinterleaved parityD0 D1 D2D3PD4 D5 D6PD7D8 D9 PD10D11D12 P D13D14D15P D16 D17D18D19D20 D21 D22D23P...............Disk ColumnsIncreasingLogicalDisk AddressesExample: write to D0, D5 uses disks 0, 1, 3, 4Problems of Disk Arrays: Small WritesD0 D1 D2D3PD0'++D0' D1 D2D3P'newdataolddataold parityXORXOR(1. Read)(2. Read)(3. Write)(4. Write)RAID-5: Small Write Algorithm1 Logical Write = 2 Physical Reads + 2 Physical Writes01/14/2019 14Spring 2011 -- Lecture #27Tech Report Read ‘Round the World(December 1987)01/14/2019 Spring 2011 -- Lecture #27 15RAID-I•RAID-I (1989) –Consisted of a Sun 4/280 workstation with 128 MB of DRAM, four dual-string SCSI controllers, 28 5.25-inch SCSI disks and specialized disk striping software01/14/2019 Spring 2011 -- Lecture #27 16RAID II•1990-1993•Early Network Attached Storage (NAS) System running a Log Structured File System (LFS)•Impact:–$25 Billion/year in 2002–Over $150 Billion in RAID device sold since 1990-2002–200+ RAID companies (at the peak)–Software RAID a standard component of modern OSs01/14/2019 17Spring 2011 -- Lecture #27RAID II01/14/2019 Spring 2011 -- Lecture #27 18RAID Summary•Logical-to-physical block mapping, parity striping, read-modify-write processing•Embedded caches and orchestrating data staging between network interfaces, parity hardware, and file server interfaces•Failed disk replacement, hot spares, background copies and backup•Embedded log-structured file systems, compression on the fly•Software complexity dominates hardware!01/14/2019 Spring 2011 -- Lecture #27 19Agenda•RAID•Administrivia•Course Summary (Randy)•Cal Culture (Dave)•Course Evaluation01/14/2019 Spring 2011 -- Lecture #27 20Administrivia•Final Review: Mon 5/2, 5 – 8PM, 2050 VLSB•Final Exam: Mon 5/9,


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Berkeley COMPSCI 61C - Redundant Arrays of Inexpensive Disks

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