Redundancy Through Hamming Code

à Disks are synchronized

à Very small stripes

à Error correction calculated across corresponding bits on disks

à Multiple parity disks store Hamming code error correction in corresponding positions.

à Lots of redundancy

à Expensive

? Not used

RAID 3

Bit-Interleaved Parity

à Similar to RAID 2

à Only one redundant disk, no matter how large the array

à Simple parity bit for each set of corresponding bits

à Data on failed drive can be reconstructed from surviving data and parity info

à Very high transfer rates

RAID 4

Block-Level Parity

z Each disk operates independently

z Good for high I/O request rate

z Large stripes

z Bit by bit parity calculated across stripes on each disk

z Parity stored on each disk

RAID 5

Block-Level Distributed Parity

z Like RAID 4

z Parity striped across all disks

z Round robin allocation for parity stripe

z Avoid RAID 4 botl-neck at parity disk

z Commonly used in network servers

RAID 6

Redundancy Through 2 Different Codes

z The scheme of functioning suggests calculation of 2 control codes stored in different blocks distributed through all disks.

z Control codes P and Q are calculated by different algorithms, it allows to restore lost data when even two disks have been failed.

z The hardware is more complicated.

Optical Memory

Optical Disk Products:

z CD

A nonerasable disk that stores digitized audio information. The standard system uses 12-cm disks and can record more than 60 minutes of uninterrupted playing time.

CD-ROM

A nonerasable disk used for storing computer data. The standard system uses 12-cm disks and can hold more than 550 Mbytes.

DVD

Digital video disk. The technology of video-signals recording and other data of a large volume is used and it?s based on methods of information (data) compression.

WORM

Write-Once Read Many is more easily written than CD-ROM, making single-copy disks commercially feasible; holds from 200 to 800 Mbytes of data.

Date: 2016-06-13; view: 50