Lecture 12 I O Introduction Storage Devices Metrics Productivity Professor David A Patterson Computer Science 252 Spring 1998 DAP Spr 98 UCB 1 Motivation 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 CPU Diminishing value of faster CPUs DAP Spr 98 UCB 2 Storage 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 Performance DAP Spr 98 UCB 3 I O Systems Processor interrupts Cache Memory I O Bus Main Memory I O Controller Disk Disk I O Controller I O Controller Graphics Network DAP Spr 98 UCB 4 Technology Trends Disk Capacity now doubles every 18 months before 1990 every 36 motnhs Today Processing Power Doubles Every 18 months Today Memory Size Doubles Every 18 months 4X 3yr The TheI O I O GAP GAP Today Disk Capacity Doubles Every 18 months Disk Positioning Rate Seek Rotate Doubles Every Ten Years DAP Spr 98 UCB 5 Storage 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 storage DAP Spr 98 UCB 6 Historical 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 interfaces DAP Spr 98 UCB 7 Disk History Data density Mbit sq in Capacity of Unit Shown Megabytes 1973 1 7 Mbit sq in 140 MBytes 1979 7 7 Mbit sq in 2 300 MBytes source New York Times 2 23 98 page C3 Makers of disk drives crowd even mroe data into even smaller spaces DAP Spr 98 UCB 8 Historical 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 9 Disk History 1989 63 Mbit sq in 60 000 MBytes 1997 1450 Mbit sq in 2300 MBytes 1997 3090 Mbit sq in 8100 MBytes source New York Times 2 23 98 page C3 Makers of disk drives crowd even mroe data into even smaller spaces DAP Spr 98 UCB 10 MBits per square inch DRAM as of Disk over time 9 v 22 Mb si 40 35 30 25 20 15 470 v 3000 Mb si 10 5 0 2 v 1 7 Mb si 0 1974 1980 1986 1992 1998 source New York Times 2 23 98 page C3 Makers of disk drives crowd even mroe data into even smaller spaces DAP Spr 98 UCB 11 Alternative Data Storage Technologies Early 1990s Cap Technology MB Conventional Tape Cartridge 25 150 IBM 3490 5 800 BPI TPI 12000 22860 104 38 43200 61000 1638 1870 Magnetic Optical Disk Hard Disk 5 25 1200 33528 IBM 3390 10 5 3800 27940 Sony MO 5 25 640 Helical Scan Tape Video 8mm 4600 DAT 4mm 1300 24130 BPI TPI Data Xfer Access Million KByte s Time 1 2 0 9 92 3000 minutes seconds 71 114 492 183 45 secs 20 secs 1880 2235 63 62 3000 4250 18796 454 88 18 ms 20 ms 100 ms DAP Spr 98 UCB 12 Purpose Devices Magnetic Disks Long term nonvolatile storage Large inexpensive slow level in the storage hierarchy Track Sector Characteristics Cylinder 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 Head Platter 7200 RPM 120 RPS 8 ms per rev ave rot latency 4 ms 128 sectors per track 0 25 ms per sector 1 KB per sector 16 MB s Response time Queue Controller Seek Rot Xfer Service time DAP Spr 98 UCB 13 Disk Device Terminology Disk Latency Queuing Time Controller time Seek Time Rotation Time Xfer Time Order of magnitude times for 4K byte transfers Seek 8 ms or less Rotate 4 2 ms 7200 rpm Xfer 1 ms 7200 rpm DAP Spr 98 UCB 14 Advantages of Small Formfactor Disk Drives Low cost MB High MB volume High MB watt Low cost Actuator Cost and Environmental Efficiencies DAP Spr 98 UCB 15 CS 252 Administrivia Wed March 4 Quiz 1 Pizza at LaVal s 8 30 10PM Email URL of initial project home page to TA can share some knowledge gained with other projects allow faculty TA to make suggestoins final report will be a URL Limit access to cs berkeley for now Upcoming events in CS 252 13 Mar Fri I O 2 Queuing Theory and Busses 18 Mar Wed I O 3 Tertiary Storage Network Intro 20 Mar Fri Networks 2 Interface Switches Routing 23 Mar to 27 Mar Spring Break DAP Spr 98 UCB 16 Tape vs Disk Longitudinal tape uses same technology as hard disk tracks its density improvements Disk head flies above surface tape head lies on surface Disk fixed tape removable Inherent cost performance based on geometries fixed rotating platters with gaps random access limited area 1 media reader vs removable long strips wound on spool sequential access unlimited length multiple reader New technology trend Helical Scan VCR Camcoder DAT Spins head at angle to tape to improve density DAP Spr 98 UCB 17 Current Drawbacks to Tape Tape wear out Helical 100s of passes to 1000s for longitudinal Head wear out 2000 hours for helical Both must be accounted for in economic reliability model Long rewind eject load spin up times not inherent just no need in marketplace so far Designed for archival DAP Spr 98 UCB 18 Automated Cartridge System STC 4400 8 feet 10 feet 6000 x 0 8 GB 3490 tapes 5 TBytes in 1992 500 000 O E M Price 6000 x 10 GB D3 tapes 60 TBytes in 1998 Library of Congress all information in the world in
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