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Understanding Parity It is through continuous redundancy of as many parts of the entire system that RAID offers security against data loss, data access, and component failure. Parity is simply a method of safeguarding data against corruption and loss. The parity stored by a RAID controller is the redundancy implemented in the read/write data storage component to the array. RAID controllers calculate and store an additional data block to every write to the storage system in response to user requests. This additional parity data is what allows reconstruction of the entire logical volume in the event of a single component failure such as a hard drive. Data redundancy is therefore synonymous with data parity when relating to RAID array systems. The most simplistic method of data security is to keep a second copy of all your data separate from the original source. For example, a 4GB hard drive could be mirrored onto another 4GB hard drive. This produces a perfect carbon copy of the original data, and in the event of a single hard drive failure, the data would still be readily available. This simple form of data security carries a high cost factor though. As the amount or quantity of data increases the cost of storing it increase by a multiple of two. In a server environment with multiple clients and a large quantity of data the cost of storing data this way would be uneconomical. It would also be extremely time consuming to administer. Parity is a more cost effective manner in which to safeguard data against transmission loss and corruption. As data is transmitted across any physical media such as a network, when it is stored in physical memory, RAID arrays, or even on hard drives or tapes, there needs to be some safety measure in force to ensure that the data that arrives at the destination is the same as the data that was sent. With data parity implementation it is not necessary to keep an entire copy of the data as detailed in the first paragraph. This seriously reduces the cost of data security. At its simplest, parity is a method that enables a computer to detect errors in the data being received. Higher forms of parity combine this facility with the ability to correct certain errors in the data. Related topics:
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