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Software Raid partitioning

Posted on 2008-10-21
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HI,
I am trying to understand a cocept for raid pertition.
i know there are hardware raid which i am using right now
but i want to use software raid for another linux pc

I understand, if i have only 1 hard drive, then its useless if i try to configure software raid.
suppose , if i have 3 hardrive of diffrent size,
can i make it RAid 5 ??

or there is any requirement for Raid1 , Raid 4 and Raid 5 ??

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Question by:fosiul01
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by:knightfox
ID: 22766056
Wikipedia provides more than y ou could ever want on RAID.

http://en.wikipedia.org/wiki/RAID

In short RAID levels are:-

RAID 0 (striped disks) distributes data across several disks in a way that gives improved speed and full capacity, but all data on all disks will be lost if any one disk fails.

RAID 1 (mirrored disks) could be described as a backup solution, using two (possibly more) disks that each store the same data so that data is not lost as long as one disk survives. Total capacity of the array is just the capacity of a single disk. The failure of one drive, in the event of a hardware or software malfunction, does not increase the chance of a failure nor decrease the reliability of the remaining drives (second, third, etc).

RAID 5 (striped disks with parity) combines three or more disks in a way that protects data against loss of any one disk; the storage capacity of the array is reduced by one disk.

RAID 6 (less common) can recover from the loss of two disks.

RAID 10 (or 1+0) uses both striping and mirroring.

Where possible I always use a hardware RAID as it runs from a RAID controller which is independant of the OS, Software RAID will use system resource to process data.

This has been discussed many times

http://www.experts-exchange.com/Storage/Storage_Technology/Q_23622045.html

http://www.experts-exchange.com/OS/Linux/Q_21760459.html

http://whitepapers.zdnet.co.uk/0,1000000651,260285584p,00.htm

/Fox

/Fox
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by:fosiul01
ID: 22766402
HI thanks for those links

just one thing,##
as i said, i have 3 harddisk attached to linux box
now if i want to implement raid 5

does it need same size of hardrive  ??
currentluy , one is 10 GB + 10GB + 80 GB

will i be able to install raid 5 software  ??
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knightfox earned 2000 total points
ID: 22766788
no.. all drives needs to be the same size and speed for RAID 5 to work as you have one drive for parity and two usabe for storage.

/Fox
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by:fosiul01
ID: 22766891
yah i have done that one just little before

http://www.linuxtopia.org/online_books/centos5/centos5_administration_guide/centos5_s1-raid-config.html

thanks for the help. i will close this question.

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by:__geof__
ID: 22768608
So the answer are yes. You can have a RAID 5 with 3 drives. And there are requirements for RAID.

I want to add a comment to the very good answer from knightfox. I see you mentioned RAID 4 (and it is not explained in the answer above). I have never seen a RAID 4. Usually people choose RAID 5 instead.
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