ch11 - Database System Concepts, 5th Ed . Silberschatz,...

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Unformatted text preview: Database System Concepts, 5th Ed . Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-use Chapter 11: Storage and File Structure Chapter 11: Storage and File Structure Rev. Aug 1, 2008 Silberschatz, Korth and Sudarshan 11.2 Database System Concepts - 5 th Edition Chapter 11: Storage and File Structure Chapter 11: Storage and File Structure Overview of Physical Storage Media Magnetic Disks RAID Tertiary Storage Storage Access File Organization Organization of Records in Files Data-Dictionary Storage Silberschatz, Korth and Sudarshan 11.3 Database System Concepts - 5 th Edition Classification of Physical Storage Media 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 battery-backed up main-memory. Silberschatz, Korth and Sudarshan 11.4 Database System Concepts - 5 th Edition Physical Storage Media Physical Storage Media Cache fastest and most costly form of storage; volatile; managed by the computer system hardware (Note: Cache is pronounced as cash) 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. Silberschatz, Korth and Sudarshan 11.5 Database System Concepts - 5 th Edition Physical Storage Media (Cont.) 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 (10K 1M) 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 Silberschatz, Korth and Sudarshan 11.6 Database System Concepts - 5 th Edition Physical Storage Media (Cont.) Physical Storage Media (Cont.) Flash memory NOR Flash Fast reads, very slow erase, lower capacity...
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ch11 - Database System Concepts, 5th Ed . Silberschatz,...

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