AN OVERVIEW OF AN OVERVIEW OF PHYSICAL STORAGE PHYSICAL STORAGE

MEDIAMEDIADATABASE MANAGEMENT DATABASE MANAGEMENT

SYSTEMSSYSTEMS

1.Several types of data storage exist in most 1.Several types of data storage exist in most computer systems. They vary in speed of computer systems. They vary in speed of access, cost per unit of data, and reliability.access, cost per unit of data, and reliability.

CacheCache : : most costly and most costly and fastest form of storagefastest form of storage. .

Usually very small, and managed by the Usually very small, and managed by the operating system. operating system.

Main Memory (MM):Main Memory (MM): the storage area for data the storage area for data available to be operated on. available to be operated on. General-purpose machine instructionsGeneral-purpose machine instructions

operate on main memory. operate on main memory. Contents of main memory are usually lost in a Contents of main memory are usually lost in a

power failure or ``crash''. power failure or ``crash''. Usually too small (even with megabytes) and Usually too small (even with megabytes) and

too too expensive to store the entire databaseexpensive to store the entire database. .

Flash memoryFlash memory:: EEPROM ( EEPROM (electrically erasable electrically erasable programmable read-only memoryprogrammable read-only memory). ).

Data in flash memory survive from power Data in flash memory survive from power failure. failure.

Reading data from flash memory takes about Reading data from flash memory takes about 10 10 nano-secsnano-secs (roughly as fast as from main (roughly as fast as from main memory), and writing data into flash memory is memory), and writing data into flash memory is more complicated: write-once takes about 4-10 more complicated: write-once takes about 4-10 microsecs. microsecs.

To overwrite what has been written, one has to To overwrite what has been written, one has to first erase the entire bank of the memory. It first erase the entire bank of the memory. It may support only a may support only a limited number of erase limited number of erase cyclescycles ( to ). ( to ).

It has found its popularity as a It has found its popularity as a replacement for replacement for disksdisks for storing small volumes of data (5-10 for storing small volumes of data (5-10 megabytesmegabytes).).

FLASH STORAGEFLASH STORAGE

Flash USB driveFlash USB drive A flash USB drive is a memory storage A flash USB drive is a memory storage

unit, using its own 'flash' memory type, unit, using its own 'flash' memory type, contrast to magnetic disks used... contrast to magnetic disks used...

Compactflash Compactflash The Memory Stick Duo, which is The Memory Stick Duo, which is

slightly smaller than the competing slightly smaller than the competing Secure Digital format, was developed Secure Digital format, was developed in response to Sony's... in response to Sony's...

FLASH STORAGEFLASH STORAGE

Microdrive Microdrive Pioneered by IBM, microdrives are Pioneered by IBM, microdrives are

minute hard disks that come in minute hard disks that come in CompactFlash Type II format and CompactFlash Type II format and typically offer larger storage... typically offer larger storage...

MMC MMC Like any flash memory card, it can be Like any flash memory card, it can be

used to store various types of files, used to store various types of files, including photos, videos, music, or... including photos, videos, music, or...

FLASH STORAGEFLASH STORAGE

MMC Memory Card MMC Memory Card A flash memory card that provides A flash memory card that provides

storage for cellphones, PDAs and other storage for cellphones, PDAs and other handheld devices. Introduced in 1997 handheld devices. Introduced in 1997 with a 4MB... with a 4MB...

Multimediacard Multimediacard A MultiMediaCard (MMC) is a tiny A MultiMediaCard (MMC) is a tiny

memory card that uses flash memory to memory card that uses flash memory to make storage portable among various make storage portable among various devices devices

Magnetic-disk storageMagnetic-disk storage::

primary medium for long-term storageprimary medium for long-term storage.. Typically the Typically the entire database is stored on diskentire database is stored on disk. . Data must be Data must be moved from disk to main moved from disk to main

memorymemory in order for the data to be operated in order for the data to be operated on. on.

After operations are performed, data must be After operations are performed, data must be copied back to diskcopied back to disk if any changes were made. if any changes were made.

Disk storage is called Disk storage is called direct accessdirect access storage storage as it is possible to read data on the disk in any as it is possible to read data on the disk in any order (unlike sequential access). order (unlike sequential access).

Disk storage usually survives power failures Disk storage usually survives power failures and system crashes. and system crashes.

Optical storageOptical storage:: CD-ROM (compact-disk CD-ROM (compact-disk read-only memory), read-only memory), WORM (WORM (write-once read-write-once read-manymany)) disk (for archival storage of data), and disk (for archival storage of data), and Juke boxJuke box (containing a few drives and numerous (containing a few drives and numerous disks loaded on demand). disks loaded on demand).

Tape StorageTape Storage:: used primarily for backup and used primarily for backup and archival data. archival data. Cheaper, but much Cheaper, but much slower accessslower access, since tape , since tape

must be must be read sequentially from the beginningread sequentially from the beginning. . Used as Used as protection from disk failuresprotection from disk failures! !

The storage device hierarchy is presented The storage device hierarchy is presented in Figure given below, where the higher in Figure given below, where the higher levels are expensive (cost per bit), fast levels are expensive (cost per bit), fast (access time), but the capacity is smaller.(access time), but the capacity is smaller.

STORAGE HIERARCHYSTORAGE HIERARCHY

Another classification: Primary, Another classification: Primary, secondary, and tertiary storage. secondary, and tertiary storage. Primary storagePrimary storage: the fastest storage media, : the fastest storage media,

such as cash and main memory. such as cash and main memory. Secondary (or on-line) storageSecondary (or on-line) storage: the next level : the next level

of the hierarchy, e.g., magnetic disks. of the hierarchy, e.g., magnetic disks. Tertiary (or off-line) storageTertiary (or off-line) storage: magnetic tapes : magnetic tapes

and optical disk juke boxes. and optical disk juke boxes. Volatility of storageVolatility of storage. . Volatile storageVolatile storage loses loses

its contents when the power is removed. its contents when the power is removed. Without power backup, data in the Without power backup, data in the volatile storage (the part of the hierarchy volatile storage (the part of the hierarchy from main memory up) must be written to from main memory up) must be written to nonvolatile storage for safekeeping. nonvolatile storage for safekeeping.

ISSUES ON ISSUES ON CLASSIFICATIONCLASSIFICATION

Issues are Issues are speed, cost, reliabilityspeed, cost, reliability • • Media types:Media types: – – Primary storagePrimary storage (volatile): Cache, (volatile): Cache,

Main MemoryMain Memory – – Secondary or On-line storage (non-Secondary or On-line storage (non-

volatile):volatile): Flash Memory, Mag Disk Flash Memory, Mag Disk – – Tertiary or Off-line storageTertiary or Off-line storage (non- (non-

volatile): Optical Storage, Tape volatile): Optical Storage, Tape StorageStorage

SECONDARY STORAGESECONDARY STORAGE

TERTIARY STORAGETERTIARY STORAGE