Wednesday, October 15, 2008

Multimedia Storage Devices

Multimedia storage and retrieval
Magnetic media technology

  • hard disk
  • Redundant Array of Inexpensive Disks (RAID)

  • Optical media technology
  • large capacity but slower access near-line mass-storage (jukeboxes)
  • CD-ROM
  • CD-WORM
  • CD-WR (erasable CD)


  • CD-ROM
    CD-ROM - Compact Disc Read Only memory.
    CD-ROM has several advantages and few disadvantages.

    Advantages:
    a) CD-ROM can hold about 650 megabytes of data, the equivalent of thousands of floppy disc.
    b) CD-ROM are not damaged by magnetic fields or the x-rays.
    c) The data on a CD-ROM can be accessed much faster than on a tape.

    Disadvantage :
    CD-ROM are 10 to 20 times slower than hard discs.

    CD-ROM Capacity
    The capacity of a CD-ROM depends on the drive.
    Almost all CD-ROM drives will handle up to 620 megabytes without any problems.
    Many newer drives can read discs with over 700 megabytes.
    The fundamental unit of data on a CD-ROM is the sector.
    Every CD-ROM is composed of a given amount of a sector.

    Example of Storage in Multimedia
    • CD-RW Rewritable Compact Discs
      • Rewritable-- Data can be Overwritten Directly and Repeatedly
      • 650MB Storage Capacity/74 Minutes Digital Audio Recording Time
      • Playable on All CD-ROM Drives With MultiRead Functionality
    • CD-R Recordable Compact Discs;
      • Offer high-density storage and superior audio recording.
      • 650MB/ 74 Min. Capacity


    RAID Technology
    RAID = Redundant Array of Inexpensive Disks.
  • RAID is a new technology that provides a potential alternative to mass storage combined with high throughput and reliability.
  • It is a set of disk drives viewed by the user as one or more logical drives.
  • Data is distributed across the set of drives in a pre-defined manner.

  • There are 8 discrete levels of RAID functionality
    1) Level 0 : Disk Striping
    2) Level 1 : Disk Mirroring
    3) Level 2 : Bit Interleaving and Header Error Correction (HEC) Parity
    4) Level 3 : Bit Interleaving and XOR Parity
    5) Level 4 : Block Interleaving with XOR Parity
    6) Level 5 : Block Interleaving with Parity Distribution
    7) Level 6 : Fault tolerant system
    8) Level 7 : Heterogeneous system

    1) RAID Level 0 - Disk Striping

    Disk Striping for RAID Level 0

    RAID Level 0 is based on distribution of data across multiple drives connected to a single disk controller

    Characteristics/Advantages
    1) RAID 0 implements a striped disk array, the data is broken down into blocks and each block is written to a
    separate disk drive.
    2) I/O performance is greatly improved by spreading the I/O load across many channels and drives
    3) Best performance is achieved when data is striped across
    multiple controllers with only one drive per controller

    2) RAID Level 1 - Disk Mirroring

    Disk Layout in RAID Level 1

    RAID Level 1 focuses on fault tolerance in addition to striping. Disk Layout in RAID Level 1

    3) RAID Level 2 - Bit Interleaving and HEC Parity

    RAID 2 disk subsystem contain multiple drives connected to a disk controller, with either single or multiple channels.

    4) RAID Level 3 - Bit Interleaving with XOR Parity

    RAID 3 introduces parity to the model by interleaving the data at a bit level across several drives similar to data striping.

    5) RAID Level 4 - Block Interleaving with XOR Parity

    Very similar to RAID 3 except that striping is done at block level across several drives.

    6) RAID Level 5 - Block Interleaving with Parity Distribution

    Parity is distributed across various drives.
    Removing a potential bottleneck.

    7) RAID level 6 - Fault-Tolerant System

    Improvement over RAID 5 model through the addition error recovery information.

    8) RAID Level 7 - Heterogeneous System

    Allows each individual drive to access data as fast as possible by incorporating a few crucial features.

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