**one**of the input bits is a 1. This is the resulting truth table:

1 xor 0 = 1 1 xor 1 = 0 0 xor 1 = 1 0 xor 0 = 0

What makes raid 5 work is that xor have the following interesting property:

If A xor B = X then A xor X = B

And this works with any number of inputs:

X = A xor B xor C xor D xor E A = X xor B xor C xor D xor E B = A xor X xor C xor D xor E C = A xor B xor X xor D xor E D = A xor B xor C xor X xor E E = A xor B xor C xor D xor X

Simply exchange the letter of the data that you want back by replacing that with the x. In a raid array, the x would be the parity drive. This is why you only loose one disc worth of storage space in a raid 5 setup, no matter how many hard drives you put in.

## No comments:

Post a Comment