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RAID 1 and RAID 5

Last response: in Storage
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July 29, 2012 5:49:47 AM

Hello,

Lets say that we have an array of disks. It has n disks and is fault tolerant.

RAID 1: n=2; data on the first disk is identical to the second disk. disk0=disk1
RAID 5: n>=3; all disk in the array are XOR'ed to the last disk for parity. diskn=xor(disk0...diskn-1)

It is my understanding in a RAID 1 that the data on the second disk is identical to the first, also the data on the second disk is equal to the XOR of the first disk; disk1=disk0 and disk1=xor(disk0).

If the second disk in a RAID 1 is identical to the parity of the first, therefore RAID 1 is a RAID 5 with only two drives.

Did I come to the wrong conclusion? Also, I don't care what the standard definition of a RAID 5 happens to be. If I can get a controller to use RAID 5 with only two disks, then this is true?

Regards,

Ryan

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a c 87 G Storage
July 29, 2012 5:55:30 AM

What you're describing are RAID 1 and RAID 4

RAID 5 is identical to RAID 4 except that the parity block is distributed across all disks so that each of n disks has n-1 data blocks and 1 parity block.

RAID 6 is similar except that RAID 6 has n-2 data blocks on each disk and 2 parity blocks

A controller with RAID 5 on only 2 disks would be identical to RAID 1

EDIT: for comparison

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