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Lecture_20 - Chapter 6 Storage and Other I/O Topics I/O...

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Chapter 6 Storage and Other I/O Topics
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Chapter 6 — Storage and Other I/O Topics — 2 Introduction I/O devices can be characterized by Behaviour: input, output, storage Partner: human or machine Data rate: bytes/sec, transfers/sec I/O bus connections §6.1 Introduction
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Chapter 6 — Storage and Other I/O Topics — 3 I/O System Characteristics Dependability is important Particularly for storage devices Performance measures Latency (response time) Throughput (bandwidth) Desktops & embedded systems Mainly interested in response time & diversity of devices Servers Mainly interested in throughput & expandability of devices
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Chapter 6 — Storage and Other I/O Topics — 4 Dependability Fault: failure of a component May or may not lead to system failure §6.2 Dependability, Reliability, and Availability Service accomplishment Service delivered as specified Service interruption Deviation from specified service Failure Restoration
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Chapter 6 — Storage and Other I/O Topics — 5 Dependability Measures Reliability: mean time to failure (MTTF) Service interruption: mean time to repair (MTTR) Mean time between failures MTBF = MTTF + MTTR Availability = MTTF / (MTTF + MTTR) Improving Availability Increase MTTF: fault avoidance, fault tolerance, fault forecasting Reduce MTTR: improved tools and processes for diagnosis and repair
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Chapter 6 — Storage and Other I/O Topics — 6 Disk Storage Nonvolatile, rotating magnetic storage §6.3 Disk Storage
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Chapter 6 — Storage and Other I/O Topics — 7 Disk Sectors and Access Each sector records Sector ID Data (512 bytes, 4096 bytes proposed) Error correcting code (ECC) Used to hide defects and recording errors Synchronization fields and gaps Access to a sector involves Queuing delay if other accesses are pending Seek: move the heads Rotational latency Data transfer Controller overhead
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Chapter 6 — Storage and Other I/O Topics — 8 Disk Access Example Given 512B sector, 15,000rpm, 4ms average seek time, 100MB/s transfer rate, 0.2ms controller
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