Storage and files - Database System Concepts, 5th Ed ....

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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 ©Silberschatz, Korth and Sudarshan 11.2 Database System Concepts - 5 th Edition, Oct 23, 2005. 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 ■ Storage Structures for Object-Oriented Databases ©Silberschatz, Korth and Sudarshan 11.3 Database System Concepts - 5 th Edition, Oct 23, 2005. 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 batter- backed up main-memory. ©Silberschatz, Korth and Sudarshan 11.4 Database System Concepts - 5 th Edition, Oct 23, 2005. Physical Storage Media 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. ©Silberschatz, Korth and Sudarshan 11.5 Database System Concepts - 5 th Edition, Oct 23, 2005. 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 ● Cost per unit of storage roughly similar to main memory ● Widely used in embedded devices such as digital cameras ● Is a type of EEPROM (Electrically Erasable Programmable Read-Only Memory) ©Silberschatz, Korth and Sudarshan 11.6 Database System Concepts - 5 th Edition, Oct 23, 2005....
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This note was uploaded on 10/25/2010 for the course CMPN SEM4 taught by Professor Thakur during the Spring '07 term at University of Mumbai.

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Storage and files - Database System Concepts, 5th Ed ....

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