Notes02 - CS245:DatabaseSystem Principles Notes02:Hardware...

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CS 245 Notes 2 1 CS 245: Database System  Principles Notes 02: Hardware Steven Whang
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CS 245 Notes 2 2 Outline  Hardware: Disks  Access Times  Example - Megatron 747  Optimizations  Other Topics: Storage costs Using secondary storage Disk failures
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CS 245 Notes 2 3 Hardware DBM S Data Storage
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CS 245 Notes 2 4 P M C Typical Computer Secondary Storage ... ...
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CS 245 Notes 2 5 Processor Fast, slow, reduced instruction set, with cache, pipelined… Speed: 100    500     1000 MIPS Memory Fast, slow, non-volatile, read-only,… Access time: 10 -6       10 -9   sec. μ s      1 ns
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CS 245 Notes 2 6 Secondary storage Many flavors: - Disk:  Floppy (hard, soft) Removable Packs Winchester Ram disks Optical, CD-ROM… Arrays - Tape Reel, cartridge Robots
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CS 245 Notes 2 7 Focus on : “Typical Disk” Terms:  Platter, Head, Actuator Cylinder, Track Sector (physical), Block (logical), Gap
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CS 245 Notes 2 8 Top View
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CS 245 Notes 2 9 Typical” Numbers Diameter:  1 inch   15 inches Cylinders: 100     2000 Surfaces: 1 (CDs)  (Tracks/cyl)    2 (floppies)   30 Sector Size: 512B    50K Capacity: 360 KB (old floppy)  2 TB 
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CS 245 Notes 2 10 Disk Access Time block x in memory ? I want block X
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CS 245 Notes 2 11 Time =  Seek Time + Rotational Delay + Transfer Time + Other
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CS 245 Notes 2 12 Seek Time 3 or 5x x 1 N Cylinders Traveled Time
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CS 245 Notes 2 13 Average Random Seek Time              SEEKTIME (i   j) S =           N(N-1)  N  N i=1 j=1 j i “Typical” S: 10 ms   40 ms
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CS 245 Notes 2 14 Rotational Delay Head Here Block I Want
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CS 245 Notes 2 15 Average Rotational Delay R = 1/2 revolution “typical” R = 8.33 ms (3600 RPM)
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CS 245 Notes 2 16 Transfer Rate:  t “typical” t:  1     3  MB/second transfer time:  block size t
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CS 245 Notes 2 17 Other Delays CPU time to issue I/O Contention for controller Contention for bus, memory “Typical” Value: 0
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CS 245 Notes 2 18 So far: Random Block Access What about: Reading “Next” block?
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CS 245 Notes 2 19 If we do things right   (e.g., Double Buffer,      Stagger Blocks…) Time to get   =  Block Size   + Negligible     block      t - skip gap - switch track - once in a while,     next cylinder
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This document was uploaded on 03/08/2011.

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Notes02 - CS245:DatabaseSystem Principles Notes02:Hardware...

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