![]() ![]() Exclusive-or parity is commonly used in storage systems as RAID-5 configuration: Given a, b, c, e and P, it is easy to reconstruct the missing block d: If the first parity bit is 0, you know that the number of 1 bits among the first bits of a, b, c, d, e is even.If any one device fails, you can still recompute the block from the failed device, and so you haven’t lost any data.Ī simple way to calculate the parity P is just to combine the values a, b, c, d, e with the exclusive-or (XOR) operator:Įffectively, every parity bit protects the corresponding bits of a, b, c, d, e. You can put the 5 data blocks on 5 different storage devices, and then store a parity block on a 6th device. As an example, say that you need to reliably store 5 data blocks of a fixed size (e.g., 4kB). Let’s start with the simple case – single parity. This article is for computer engineers who would like to have a high-level understanding of how the dual parity calculation works, without diving into all of the mathematical details. Parity protection is a common technique for reliable data storage on mediums that may fail (HDDs, SSDs, storage servers, etc.) Calculation of parity uses tools from algebra in very interesting ways, in particular in the dual parity case.
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June 2023
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