XOR

Today, i get a question about RAID 4 from my friend. Interesting point is how to recover data from 1 death disk? 

From here => http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_4

I figure out the way it works.

example, we had: 

A x B x C x D = E

problem: A was lost, how to recover A?

solve:

i had: 

A x A = 0

# x 0 = #

# x 1 = !#

so:

A x B x C x D x B x C x D = E x B x C x D

<=> A = E x B x C x D

we got A.