Lecture 12: I/O Introduction: Storage Devices, Metrics, & ProductivityMotivation: Who Cares About I/O?Storage System Issues: 1.5 weeksI/O SystemsTechnology TrendsStorage Technology DriversHistorical PerspectiveDisk HistorySlide 9Slide 10MBits per square inch: DRAM as % of Disk over timeAlternative Data Storage Technologies: Early 1990sDevices: Magnetic DisksDisk Device TerminologyAdvantages of Small Formfactor Disk DrivesCS 252 AdministriviaTape vs. DiskCurrent Drawbacks to TapeAutomated Cartridge SystemLibrary vs. StorageRelative Cost of Storage Technology—Late 1995/Early 1996Lecture OutlineDisk I/O PerformanceResponse Time vs. ProductivityResponse Time & ProductivityDisk Time ExampleSlide 27Processor Interface IssuesI/O InterfaceMemory Mapped I/OProgrammed I/O (Polling)Interrupt Driven Data TransferDirect Memory AccessInput/Output ProcessorsRelationship to Processor ArchitectureSlide 36SummarySummary: Relationship to Processor ArchitectureSummary: Storage System IssuesDAP Spr.‘98 ©UCB 1Lecture 12: I/O Introduction: Storage Devices, Metrics, & ProductivityProfessor David A. PattersonComputer Science 252Spring 1998DAP Spr.‘98 ©UCB 2Motivation: Who Cares About I/O?•CPU Performance: 60% per year•I/O system performance limited by mechanical delays (disk I/O)< 10% per year (IO per sec or MB per sec)•Amdahl's Law: system speed-up limited by the slowest part!10% IO & 10x CPU => 5x Performance (lose 50%)10% IO & 100x CPU => 10x Performance (lose 90%)• I/O bottleneck: Diminishing fraction of time in CPUDiminishing value of faster CPUsDAP Spr.‘98 ©UCB 3Storage System Issues: 1.5 weeks•Historical Context of Storage I/O•Secondary and Tertiary Storage Devices•Storage I/O Performance Measures•Processor Interface Issues•A Little Queuing Theory•Redundant Arrarys of Inexpensive Disks (RAID)•I/O Buses•ABCs of UNIX File Systems•I/O Benchmarks•Comparing UNIX File System PerformanceDAP Spr.‘98 ©UCB 4I/O SystemsProcessorCacheMemory - I/O BusMainMemoryI/OControllerDisk DiskI/OControllerI/OControllerGraphicsNetworkinterruptsinterruptsDAP Spr.‘98 ©UCB 5Technology TrendsDisk Capacity now doubles every 18 months; before1990 every 36 motnhs• Today: Processing Power Doubles Every 18 months• Today: Memory Size Doubles Every 18 months(4X/3yr)• Today: Disk Capacity Doubles Every 18 months• Disk Positioning Rate (Seek + Rotate) Doubles Every Ten Years!The I/OGAPThe I/OGAPDAP Spr.‘98 ©UCB 6Storage Technology Drivers•Driven by the prevailing computing paradigm–1950s: migration from batch to on-line processing–1990s: migration to ubiquitous computing»computers in phones, books, cars, video cameras, …»nationwide fiber optical network with wireless tails•Effects on storage industry:–Embedded storage»smaller, cheaper, more reliable, lower power–Data utilities»high capacity, hierarchically managed storageDAP Spr.‘98 ©UCB 7Historical Perspective•1956 IBM Ramac — early 1970s Winchester–Developed for mainframe computers, proprietary interfaces–Steady shrink in form factor: 27 in. to 14 in.•1970s developments–5.25 inch floppy disk formfactor (microcode into mainframe)–early emergence of industry standard disk interfaces»ST506, SASI, SMD, ESDI•Early 1980s–PCs and first generation workstations•Mid 1980s–Client/server computing –Centralized storage on file server»accelerates disk downsizing: 8 inch to 5.25 inch–Mass market disk drives become a reality»industry standards: SCSI, IPI, IDE»5.25 inch drives for standalone PCs, End of proprietary interfacesDAP Spr.‘98 ©UCB 8Disk HistoryData densityMbit/sq. in.Capacity ofUnit ShownMegabytes1973:1. 7 Mbit/sq. in140 MBytes1979:7. 7 Mbit/sq. in2,300 MBytessource: New York Times, 2/23/98, page C3, “Makers of disk drives crowd even mroe data into even smaller spaces”DAP Spr.‘98 ©UCB 9Historical Perspective•Late 1980s/Early 1990s:–Laptops, notebooks, (palmtops)–3.5 inch, 2.5 inch, (1.8 inch formfactors)–Formfactor plus capacity drives market, not so much performance»Recently Bandwidth improving at 40%/ year–Challenged by DRAM, flash RAM in PCMCIA cards»still expensive, Intel promises but doesn’t deliver»unattractive MBytes per cubic inch–Optical disk fails on performace (e.g., NEXT) but finds niche (CD ROM)DAP Spr.‘98 ©UCB 10Disk History1989:63 Mbit/sq. in60,000 MBytes1997:1450 Mbit/sq. in2300 MBytessource: New York Times, 2/23/98, page C3, “Makers of disk drives crowd even mroe data into even smaller spaces”1997:3090 Mbit/sq. in8100 MBytesDAP Spr.‘98 ©UCB 11MBits per square inch: DRAM as % of Disk over time0%5%10%15%20%25%30%35%40%1974 1980 1986 1992 1998source: New York Times, 2/23/98, page C3, “Makers of disk drives crowd even mroe data into even smaller spaces”470 v. 3000 Mb/si9 v. 22 Mb/si0.2 v. 1.7 Mb/siDAP Spr.‘98 ©UCB 12Alternative Data Storage Technologies: Early 1990sCap BPI TPI BPI*TPI Data Xfer AccessTechnology (MB) (Million) (KByte/s) TimeConventional Tape:Cartridge (.25") 150 12000 104 1.2 92 minutesIBM 3490 (.5") 800 22860 38 0.9 3000 secondsHelical Scan Tape:Video (8mm) 4600 43200 1638 71 492 45 secsDAT (4mm) 1300 61000 1870 114 183 20 secsMagnetic & Optical Disk:Hard Disk (5.25") 1200 33528 1880 63 3000 18 msIBM 3390 (10.5") 3800 27940 2235 62 4250 20 msSony MO (5.25") 640 24130 18796 454 88 100 msDAP Spr.‘98 ©UCB 13Devices: Magnetic DisksSectorTrackCylinderHeadPlatter•Purpose:– Long-term, nonvolatile storage– Large, inexpensive, slow level in the storage hierarchy•Characteristics:– Seek Time (~8 ms avg)»positional latency»rotational latency• Transfer rate–About a sector per ms (5-15 MB/s)–Blocks• Capacity–Gigabytes–Quadruples every 3 years (aerodynamics)7200 RPM = 120 RPS => 8 ms per rev ave rot. latency = 4 ms128 sectors per track => 0.25 ms per sector1 KB per sector => 16 MB / sResponse time = Queue + Controller + Seek + Rot + XferService timeDAP Spr.‘98 ©UCB 14Disk Device TerminologyDisk Latency = Queuing Time + Controller time +Seek Time + Rotation Time + Xfer TimeOrder of magnitude times for 4K byte transfers:Seek: 8 ms or lessRotate: 4.2 ms @ 7200 rpmXfer: 1 ms @ 7200 rpmDAP Spr.‘98 ©UCB 15Advantages of Small Formfactor Disk DrivesLow cost/MBHigh MB/volumeHigh MB/wattLow cost/ActuatorCost and Environmental EfficienciesDAP Spr.‘98 ©UCB 16CS 252 Administrivia•Wed March 4 Quiz 1–Pizza at LaVal’s 8:30 – 10PM•Email URL of
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