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.