chapter 9 - storage - COP 4710: Database Systems Fall 2007...

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COP 4710: Data Storage Page 1 Mark Llewellyn © COP 4710: Database Systems Fall 2007 Chapter 9 – Data Storage COP 4710: Database Systems Fall 2007 Chapter 9 – Data Storage School of Electrical Engineering and Computer Science University of Central Florida Instructor : Dr. Mark Llewellyn markl@cs.ucf.edu HEC 236, 407-823-2790 http://www.cs.ucf.edu/courses/cop4710/fall2007
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COP 4710: Data Storage Page 2 Mark Llewellyn © Classification of Physical Storage Media • Speed with which data can be accessed • Cost per unit of data • Reliability – data loss on power failure or system crash – physical failure of the storage device • Can differentiate storage into: volatile storage: loses contents when power is switched off non-volatile storage : • Contents persist even when power is switched off. • Includes secondary and tertiary storage, as well as batter-backed up main-memory.
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COP 4710: Data Storage Page 3 Mark Llewellyn © Physical Storage Media Cache – fastest and most costly form of storage; volatile; managed by the computer system hardware. Main memory : – fast access (10s to 100s of nanoseconds; 1 nanosecond = 10 9 seconds) – generally too small (or too expensive) to store the entire database • capacities of up to a few Gigabytes widely used currently • Capacities have gone up and per-byte costs have decreased steadily and rapidly (roughly factor of 2 every 2 to 3 years) – Volatile — contents of main memory are usually lost if a power failure or system crash occurs.
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COP 4710: Data Storage Page 4 Mark Llewellyn © Physical Storage Media (cont.) Flash memory – Data survives power failure – Data can be written at a location only once, but location can be erased and written to again • Can support only a limited number of write/erase cycles. • Erasing of memory has to be done to an entire bank of memory – Reads are roughly as fast as main memory – But writes are slow (few microseconds), erase is slower – Cost per unit of storage roughly similar to main memory – Widely used in embedded devices such as digital cameras – also known as EEPROM (Electrically Erasable Programmable Read-Only Memory)
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COP 4710: Data Storage Page 5 Mark Llewellyn © Magnetic-disk – Data is stored on spinning disk, and read/written magnetically – Primary medium for the long-term storage of data; typically stores entire database. – Data must be moved from disk to main memory for access, and written back for storage • Much slower access than main memory (more on this later) – direct-access – possible to read data on disk in any order, unlike magnetic tape – Hard disks vs floppy disks – Capacities range up to roughly 300+ GB currently • Much larger capacity and cost/byte than main memory/flash memory • Growing constantly and rapidly with technology improvements (factor of 2 to 3 every 2 years) – Survives power failures and system crashes • disk failure can destroy data, but is very rare Physical Storage Media (cont.)
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This note was uploaded on 02/22/2009 for the course COP 4710 taught by Professor Dr. mark llewellyn during the Fall '07 term at University of Central Florida.

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chapter 9 - storage - COP 4710: Database Systems Fall 2007...

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