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Old 01-31-2008, 11:34 AM   #1
2007fld
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RAID storage capacity calculation


I'm learning RAID 5. I know it provides redundacy and improve the read/write performance by data striping and parity. The data striping means spreading data (say, a file) on several disks.

But how does the parity work exactly? mirroring? So with a RAID system, the storage capacity is one half of the real hard disk size?
 
Old 01-31-2008, 11:50 AM   #2
colucix
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Quote:
Originally Posted by 2007fld View Post
So with a RAID system, the storage capacity is one half of the real hard disk size?
Not really. Actually if you have N disks and the smaller one has size S, the total size of the array will be
Code:
(N-1)*S
Raid 5 distributes the parity information through disks. Parity information uses an exclusive OR mechanism: it stores one extra bit to reconstruct data if one or more bits are lost. You can find a good and simple explanation here. Due to this setup if a disk is lost you can recover all data, if two disk fail simultaneously all data are lost: it is a compromise between the advantages of striping and a certain degree of redundancy.
 
  


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