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RAID 5

Posted on 2006-04-21
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Can any one briefly explain whatis RAID Level 5 and how it is distributed
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Question by:ratnaprasad123
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by:Irwin Santos
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by:thaclone
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check this one out.

RAID Level 5 combines a minimum of 3 hard drives to provide fault tolerance for your data. with raid 5 its only when 2 hard drives fail simultaneously before your completely looose all your data. If  you want to  know how the data is distributed with parity , then check the following link


RAID Level 5 minimizes the write bottlenecks of RAID Level 4 by distributing parity stripes over a series of hard drives. In doing so it provides relief to the concentration of write activity on a single drive, which in turn enhances overall system performance. The way RAID Level 5 reduces parity write bottlenecks is relatively simple. Instead of allowing any one drive in the array to assume the risk of a bottleneck, all of the drives in the array assume write activity responsibilities. The distribution frees up the concentration on a single drive, improving overall subsystem throughput. RAID Level 5's parity encoding scheme is the same as Levels 3 and 4; it maintains the system's ability to recover any lost data should a single drive fail. This can happen as long as no parity stripe on an individual drive stores the information of a data stripe on the same drive. In other words, the parity information for any data stripe must always be located on a drive other than the one on which the data resides.

thaclone
let me know if you need any further explanation
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by:Merete
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Level 5 -- Block Interleaved Distributed Parity: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance. Level 5 is one of the most popular implementations of RAID.
 RAID disk drives are used frequently on servers but aren't generally necessary for personal computers.
It is worth remembering an important point about RAID systems. Even when you use a redundancy scheme like mirroring or RAID 5 or RAID 10, you must still do regular tape backups of your system. There are several reasons for insisting on this, among them:
RAID does not protect you from multiple disk failures. While one disk is off line for any reason, your disk array is not fully redundant.
Regular tape backups allow you to recover from data loss that is not related to a disk failure. This includes human errors, hardware errors, and software errors.

RAID - Not such a clever idea for your home PC
http://www.bestpricecomputers.co.uk/reviews/home-pc-raid/

raid tuturial  Raid 1 to  Raid 50
Click on the diagram to see RAID 0 in action
http://www.acnc.com/raid.html

A bit of fun
RAID Calculator
http://www.ibeast.com/content/tools/RaidCalc/RaidCalc.asp

ahahaha
Raid explained using water bottles.
http://www.epidauros.be/raid.jpg

Merete :)
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by:victornegri
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Essentially, for every stripe (writing one block to every drive), there is one parity bit written. This parity bit can be used to recreate the data on 1 lost drive.

i.e, if you have 5 drives and each line represents a stripe:

00001
00010
00100
01000
10000
00001
etc

where the "1" represents the parity bit


Calculating the disk space lost is really easy: You lose the equivilent of one Hard Drive worth of space for parity bits (i.e. you have 3-100GB drives, you lose 100GB to parity and have 200GB for data storage). The more drives you have in RAID-5, the less loss there is (i.e. 3-100GB drives = 33% loss in space where 10-100GB drives = 10% loss in space).
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by:ratnaprasad123
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Hi victornegri ,
 What is the Parity Information i am not getting you

Thanks,
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by:micromarch
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if you want fault tollerance for your files, use raid 5. But for OS use raid 1.
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victornegri earned 600 total points
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Parity is information written to the disk that allows the RAID controller to recreate any lost information in the stripe. For example, say disk 1 went bad and was offline... on the first stripe (row) of my diagram, disks 2,3, and 4 have data on them while disk 5 has a parity bit. Using the information in the parity bit, the RAID controller can reconstruct the data that was on disk 1 therefore allowing the data that was on the drive to be accessed. On stripe 2, the info on disk 4 would be used to recreate the lost information that disk 1 had, etc.
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by:Irwin Santos
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@ratnaprasad1223...the first link I provided has all the information that you are asking.
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by:Irwin Santos
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cool. thank you!
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by:thaclone
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keep being generous
thanks
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