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Home > Archive > SQL server exams > November 2001 > Raid 5
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| naeem 2001-11-22, 12:38 am |
| While implementing RAID 5 , u need 3 hard disk at least. at each hard disk along with data some parity informations r written too.in case of any one of the hard disk failure , other 2 hard disk r able to recover its data.
now my question is
---- what kind of parity informations is?
I mean what is its structure ?
Is it some kind of backup. if this is backup then it means there will huge amount of redundatnt data (excessive amont of data repetition) | |
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| Here Is A Parity Table (Sort OF)
(Parity)
0 + 0 = 1
0 + 1 = 0
1 + 0 = 0
1 + 1 = 1
hope this helps!? | |
| colinbun 2001-11-22, 8:33 am |
| You are absolutely right about the amount of disk used in raid 5. For example, if you have only 3 disks, data is written to disks 1 & 2 to start with, with parity written to disk3. For the next read, disk 1 might have the parity data, then disk 2 and so on. As you can see, you have just lost a third of your disk size.
The whole formula is
lost space = 1 / number of disks
ie. a third for 3, a quarter for 4 and so on.
Cheers,
Colin |
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