Lecture 13 Storage and Other IO Topics

Lecture 13 Storage and Other IO Topics - Chapter 6 Storage...

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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) ± ± 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 ± Access to a sector involves ± Queuing delay if other accesses are pending ± Seek: move the heads ± Rotational latency ± Data transfer ± Controller overhead ± Disk drives include caches ± Prefetch sectors in anticipation of access ± Avoid seek and rotational delay
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Chapter 6 — Storage and Other I/O Topics — 8 Flash Storage ± Nonvolatile semiconductor storage ± 100× – 1000× faster than disk ± Smaller, lower power, more robust ± But more $/GB (between disk and DRAM) §6.4 Flash Storage
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Flash Types ± NOR flash: bit cell like a NOR gate ± Random read/write access ± Used for instruction memory in embedded systems ± NAND flash: bit cell like a NAND gate ± Denser (bits/area), but block-at-a-time access ± Cheaper per GB ± Used for USB keys, media storage, … ± Flash bits wears out after 1000’s of accesses
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Lecture 13 Storage and Other IO Topics - Chapter 6 Storage...

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