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Copyright © 2005 EMC Corporation. Do not Copy - All Rights Reserved.<br />
Symmetrix Parity RAID<br />
Vol A Vol B Vol C<br />
+<br />
Parity<br />
ABC<br />
3 Host addressable volumes<br />
Not host addressable<br />
© 2005 EMC Corporation. All rights reserved. Symmetrix Foundations - 36<br />
A Parity RAID rank is the set of logical volumes related to each other for parity protection. A data<br />
volume is presented to the host operating system and defined as a separate unit address to the host.<br />
All data volumes within a rank must be the same size and emulation such as Fixed Block<br />
Architecture (FBA) or Count Key Data (CKD).<br />
Parity RAID employs the same technique for generating parity information as many other<br />
commercially available RAID solutions, that is, the Boolean operation EXCLUSIVE OR (XOR).<br />
However, EMC’s Parity implementation reduces the overhead associated with parity computation<br />
by moving the operation from controller microcode to the hardware on the XOR-capable disk<br />
drives.<br />
Additional XOR hardware assists, built into the Symmetrix global memory directors, further<br />
distributes the XOR function throughout the system to improve performance in the regeneration<br />
mode of operation. Parity RAID is available in (3+1) or (7+1) configurations, but both of these<br />
cannot exist within the same Symmetrix. This graphic illustrates a (3+1) configuration.<br />
Symmetrix Foundations - 36
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