The RAID technology

Asslamo 3likom ,

Today I am going to share some informatio about what I AM CURRENTLY TRYING TO GET CLOSER AND DO …these capital words is a warning that I don’t have a big experince about it but ….I am trying just to share here .this doesnt mean that questions or comments are not welcomed :D. and yes .. i will talk here about RAID 0,1 and 5 only

First :What is RAID ?

RAID is: Redundant Array of Inexpensive Disks …but later mrketrs changed it into Redundant Array of Independant Disks …{v  intelegant}

RAID has many schemes /architectures named by the word RAID then a number like RAID 0 ,1,…..etc

RAID various designs always try to enhance 1 of 2 things: Reliability / performance .

RAID array: when there is multiple disks are set up to use the RAID technology they are a RAID array ……….finally the computer will see this Array as a single disk .

well,We have now 2 choices for Implementing RAID .1 is the hardware solutions and the software solution.Think of it like hardware and software firewalls .You can have a firewall device in your network or you can have a machine with s/w installed on it to turn it into a Firewall .and the applications will be the only who don’t know anything about your RAID

if you choose the h/w your operating system will not even know that you are using raid .if you used the software solution you will have to learn how to make it using your OS .I am going to write a post about that v soon inshallah .

now ,please pay attention to these 3 concepts here :

1-Mirroring : having two disks mirrored means that you are writing identical data to more than one disk.

2-Striping: means splitting data across more than one disk

3-Error correction: simply ,there is a redundant data stored to allow problems to be detected and POSSIBLY repaired .

please again and again don’t continue reading this unless you understand these 3 words:mirroring,stripping and Error correction .if not go back /search …..and so

From here I will begin talking about RAID levels .open this link now and find the table which compares different levels of RAID ..don’t close it but keep it opened  in another tab in your browser and continue reading my words here

RAID 0   {Stripped disks} :

It distribues data across multiple disks ,so if we have disk0 and disk1 in RAID0 this means that the data is written to the 2 H.Ds in the same time which means  better performance .but this mean that we dont have another copy of data written here …if 1 of the 2 disks fail you lose ALL THE DATA ON THE 2 disks{ALL the data saved to the array simply}.

Now: Can I add additional hard disk to the this RAID0 ??yes ,logicically why not?? 😀

RAID1:

RAID1 mirrors the contents of the disks {1:1}..the contents of each disk is identical .data written here,here and there …lets think here …do we have incresed perofrmance??no ..ok do we have better avaiablilty? efcourse yes ….look at the table in the posted before link .

RAIND5:

here You will need>2 disks .at least 3 .simply what happens in RAID5 is Strped set with ditributed parity or interactive parity This requires all drives but one to be present to operate .This maens that single disk failure wont be a problem .you can recover and replace later but…its failure will affect the performance .

Well .I have now to thank wikipedia v v v v much as it was my reference in writing this …actually you can say that this is just some quotes of the RAID page here [http://en.wikipedia.org/wiki/Redundant_array_of_independent_disks]

Now I am going to write a Topic about : Linux software RAID

thank you

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