I understand what parity is (Sort of): A data recovery mechanism where missing data is calculated based on the data that exists. However i have encountered terminology which i can't define or put into perspective of the RAID system.This terminology is 'dedicated' and 'distributed' Parity. Now i imagine that it is somehow related to the distribution of data among separate disks, but can anyone give a more detailed definition and explanation of 'Dedicated' and 'Distributed' parity?Thanks in advance.
RAID: dedicated and distributed parity
data structures
The answer to your question can be infered from the wWikipedia page onStandard RAID levels.Parity is just one simple case of techniques for error detection, and the nameseems to be used here to stand for various techniques of errordetection and correction.The idea of dedicated vs distributed parity, is related to whether theredundancy of information is on a special dedicated disk or whether itis distributed over all disks of the RAID system.This does not apply to RAID 1 where redundancy is achieved by simpleduplication of Data.In the case of RAID 3 (and apparently RAID 2), data is striped (readspread for faster access) over several disk why the redundancy data(parity bytes or bits) is in a separate dedicated disk.In the case of RAID 5, the redundancy is spread over all the disks and mixed into the original base data(distributed parity) so that the original data can be retrievedfrom any set of n-1 disks, when any one of the n disks fails. Thecontent of the failed disk can be recomputed from the n-1 others.Distributed parity seems to be preferred to dedicated parity, though thewikipedia page is not really clear as to why. My own suspicion is thatit allows for more effective error correction than dedicated parity, which keeps the original data and the redundancy (parity) data separate.But this should be checked.