Chapter 11: Storage and File StructureChapter 11: Storage and File StructureClassification of Physical Storage MediaPhysical Storage MediaPhysical Storage Media (Cont.)Slide 6Slide 7Slide 8Storage HierarchyStorage Hierarchy (Cont.)Magnetic Hard Disk MechanismMagnetic DisksMagnetic Disks (Cont.)Disk SubsystemPerformance Measures of DisksPerformance Measures (Cont.)Optimization of Disk-Block AccessOptimization of Disk Block Access (Cont.)Slide 19RAIDImprovement of Reliability via RedundancyImprovement in Performance via ParallelismRAID LevelsRAID Levels (Cont.)Slide 25Slide 26Slide 27Slide 28Choice of RAID LevelChoice of RAID Level (Cont.)Hardware IssuesHardware Issues (Cont.)Optical DisksMagnetic TapesStorage AccessBuffer ManagerBuffer-Replacement PoliciesBuffer-Replacement Policies (Cont.)File OrganizationFixed-Length RecordsFree ListsVariable-Length RecordsVariable-Length Records: Slotted Page StructureOrganization of Records in FilesSequential File OrganizationSequential File Organization (Cont.)Multitable Clustering File OrganizationMultitable Clustering File Organization (cont.)Data Dictionary StorageData Dictionary Storage (Cont.)End of Chapter 11Record RepresentationFile Containing account RecordsFile of Figure 11.6, with Record 2 Deleted and All Records MovedFile of Figure 11.6, With Record 2 deleted and Final Record MovedByte-String Representation of Variable-Length RecordsClustering File StructureClustering File Structure With Pointer ChainsThe depositor RelationThe customer RelationSlide 61Slide 62Figure 11.4Figure 11.7Figure 11.8Figure 11.100Figure 11.20Slide 68Fixed-Length RepresentationPointer MethodPointer Method (Cont.)Mapping of Objects to FilesMapping of Objects to Files (Cont.)Management of Persistent PointersManagement of Persistent Pointers (Cont.)Hardware SwizzlingSlide 77Hardware Swizzling (Cont.)Slide 79Slide 80Slide 81Slide 82Disk versus Memory Structure of ObjectsLarge ObjectsModifying Large ObjectsDatabase System Concepts, 5th Ed.©Silberschatz, Korth and SudarshanSee www.db-book.com for conditions on re-use Chapter 11: Storage and File StructureChapter 11: Storage and File Structure©Silberschatz, Korth and Sudarshan11.2Database System Concepts - 5th Edition, Oct 23, 2005.Chapter 11: Storage and File StructureChapter 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 Sudarshan11.3Database System Concepts - 5th Edition, Oct 23, 2005.Classification of Physical Storage MediaClassification 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 Sudarshan11.4Database System Concepts - 5th Edition, Oct 23, 2005.Physical Storage MediaPhysical 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 Sudarshan11.5Database System Concepts - 5th 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 Sudarshan11.6Database System Concepts - 5th Edition, Oct 23, 2005.Physical Storage Media (Cont.)Physical Storage Media (Cont.)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Capacities range up to roughly 400 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 rare©Silberschatz, Korth and Sudarshan11.7Database System Concepts - 5th Edition, Oct 23, 2005.Physical Storage Media (Cont.)Physical Storage Media (Cont.)Optical storage non-volatile, data is read optically from a spinning disk using a laser CD-ROM (640 MB) and DVD (4.7 to 17 GB) most popular formsWrite-one, read-many (WORM) optical disks used for archival storage (CD-R, DVD-R, DVD+R)Multiple write versions also available (CD-RW, DVD-RW, DVD+RW, and DVD-RAM)Reads and writes are slower than with magnetic disk Juke-box systems, with large numbers of removable disks, a few drives, and a mechanism for automatic loading/unloading of disks available for storing large volumes of data©Silberschatz, Korth and Sudarshan11.8Database System Concepts - 5th Edition, Oct 23, 2005.Physical Storage Media (Cont.)Physical Storage Media (Cont.)Tape storage non-volatile, used primarily for backup (to recover from disk failure), and for archival datasequential-access – much slower than disk very high capacity (40 to 300 GB tapes available)tape can be removed