L14%20IO%20_%20Interfaces

L14%20IO%20_%20Interfaces - Topic 14 I/Os and Their...

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I/Os and Their Interfaces Topic 14
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Chapter 6 — Storage and Other I/O Topics — 2 Introduction ± I/O devices can be characterized by ± Behavior: input, output, storage ± Partner: human or machine ± Data rate: bytes/sec, transfers/sec ± I/O bus connections
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Chapter 6 — Storage and Other I/O Topics — 3 I/O System Characteristics ± Dependability ± Very important ± Particularly for storage devices ± Performance measures ± Latency (response time) ± Desktops & embedded systems – mainly interested in response time & diversity of devices ± Throughput (bandwidth) ± Servers – mainly interested in throughput & expandability of devices
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Chapter 6 — Storage and Other I/O Topics — 4 Two System States ± Fault: failure of a component ± May or may not lead to system failure 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 ± Dependability ± Reliability ± Availability ± Measures ± Mean time to failure (MTTF) - service accomplishment - Reliability ± Mean time to repair (MTTR) - service interruption ± 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
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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 Performance Issues ± Smart disk controller to create a simpler interface ± Microprocessor inside ± Allocate physical sectors on disk for data transfer ± Present logical sector interface to host ± Control interfaces: SCSI, ATA, SATA ± Disk controllers include caches ± Write through ± Do not update on write miss ± Prefetch sectors in anticipation of access ± Avoid seek and rotational delay
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L14%20IO%20_%20Interfaces - Topic 14 I/Os and Their...

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