MESSAGE
| DATE | 2014-12-06 |
| FROM | Ruben Safir
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| SUBJECT | Subject: [LIU Comp Sci] Parity Bit Algebra
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From owner-learn-outgoing-at-mrbrklyn.com Sat Dec 6 17:49:47 2014
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Date: Sat, 06 Dec 2014 22:50:26 +0000
From: Ruben Safir
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To: learn-at-nylxs.com, Samir Iabbassen
Subject: [LIU Comp Sci] Parity Bit Algebra
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This is from theidiscussion of Raid 3 Stallings Text which the slide
come from. It is related to the problem you asked about the parity bit
calculation for the Hamming Code
Not the methodology for logical calculation, it is straight math
Note that X is XOR for whatever UFT reason
REDUNDANCY In the event of a drive failure, the parity drive is accessed
and data is reconstructed from the remaining devices. Once the failed
drive is replaced, the missing data can be restored on the new drive and
operation resumed.
Data reconstruction is simple. Consider an array of five drives in which
X0 through X3 contain data and X4 is the parity disk.The parity for the
ith bit is calculated as follows:
X4(i) = X3(i) { X2(i) { X1(i) { X0(i)
where { is exclusive-OR function.
Suppose that drive X1 has failed. If we add X4(i) { X1(i) to both sides
of the preceding equation, we get
X1(i) = X4(i) { X3(i) { X2(i) { X0(i)
file:///home/ruben/william stallings - computer organization and
architecture designing for performance (8th edition).pdf
Page 202
http://www.nylxs.com/images/raid3_parity_math.png
Ruben
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