CS152 Computer Architecture and Engineering Lecture 24 I/O Systems IIThe Big Picture: Where are We Now?Outline of Today’s LectureReview: I/O System Design IssuesTechnology TrendsStorage Technology DriversHistorical PerspectiveDisk HistorySlide 9Slide 10MBits per square inch: DRAM as % of Disk over timeNano-layered Disk HeadsReview: Disk Device TerminologyReview: Disk Time ExampleReview: Simple Producer-Server ModelReview: Disk I/O PerformanceResponse Time vs. ProductivityResponse Time & ProductivityAdministriviaComputers in the News: Electronic InkComputers in the News: Logarithmic Computation7 Talk Commandments for a Bad TalkFollowing all the commandmentsAlternatives to a Bad TalkInclude in your final presentationIntroduction to Queueing TheoryA Little Queuing Theory: NotationA Little Queuing Theory: Use of random distributionsA Little Queuing Theory: Variable Service TimeA Little Queuing Theory: Average Wait TimeA Little Queuing Theory: M/G/1 and M/M/1A Little Queuing Theory: An ExampleGiving Commands to I/O DevicesMemory Mapped I/OI/O Device Notifying the OSI/O InterruptExample: Device InterruptAlternative: PollingPolling: Programmed I/OPolling is faster/slower than InterruptsDelegating I/O Responsibility from the CPU: DMADelegating I/O Responsibility from the CPU: IOPResponsibilities of the Operating SystemOperating System RequirementsOS and I/O Systems Communication RequirementsNetwork Attached StorageManufacturing Advantages of Disk ArraysSmall # of Large Disks Large # of Small Disks!Array ReliabilityRedundant Arrays of DisksRAID 1: Disk Mirroring/ShadowingRAID 3: Parity DiskRAID 5+: High I/O Rate ParityProblems of Disk Arrays: Small WritesHewlett-Packard (HP) AutoRAIDSubsystem OrganizationSystem Availability: Orthogonal RAIDsSystem-Level AvailabilitySummary:5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.1CS152Computer Architecture and Engineering Lecture 24I/O Systems IIMay 5, 1999John Kubiatowicz (http.cs.berkeley.edu/~kubitron)lecture slides: http://www-inst.eecs.berkeley.edu/~cs152/5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.2The Big Picture: Where are We Now?ControlDatapathMemoryProcessorInputOutput°Today’s Topic: I/O SystemsControlDatapathMemoryProcessorInputOutputNetwork/Bus5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.3Outline of Today’s Lecture°Historical discussion of Disks°A More queueing theory.°Interfacing between processor and I/O devices°RAID disk arrays°Summary5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.4Review: I/O System Design IssuesProcessorCacheMemory - I/O BusMainMemoryI/OControllerDisk DiskI/OControllerI/OControllerGraphicsNetworkinterrupts•Performance•Expandability•Resilience in the face of failure5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.5Disk Capacity now doubles every 18 months; before1990 every 36 months• 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/OGAPTechnology Trends5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.6°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 storageStorage Technology Drivers5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.7°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 interfacesHistorical Perspective5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.8Data 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”Disk History5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.9°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 performance (e.g., NEXT) but finds niche (CD ROM)Historical Perspective5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.101989:63 Mbit/sq. in60,000 MBytes1997:1450 Mbit/sq. in2300 MBytessource: New York Times, 2/23/98, page C3, “Makers of disk drives crowd even more data into even smaller spaces”1997:3090 Mbit/sq. in8100 MBytesDisk History5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.110%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 more data into even smaller spaces”470 v. 3000 Mb/si9 v. 22 Mb/si0.2 v. 1.7 Mb/siMBits per square inch: DRAM as % of Disk over time5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.12Nano-layered Disk Heads°Special sensitivity of Disk head comes from “Giant Magneto-Resistive effect” or (GMR) °IBM is leader in this technology•Same technology as TMJ-RAM breakthrough we described in earlier class. Coil for writing5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.13Disk Latency = Queueing Time + Controller time + Seek Time + Rotation Time + Xfer TimeOrder of magnitude times for 4K byte transfers:Average Seek: 8 ms or lessRotate: 4.2 ms @ 7200 rpmXfer: 1 ms @ 7200 rpmReview: Disk Device Terminology5/5/99 ©UCB Spring 1999CS152 / Kubiatowicz Lec24.14°Disk Parameters:•Transfer size is 8K bytes•Advertised average seek is 12 ms•Disk spins at 7200 RPM•Transfer rate is 4
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