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Contemporary disc systems of RAID

RAID-3. A segment is physically located on the first drive, V-segment on the second disc in the same place as X segment is placed on the third disc, segment 0-following the A segment on the first drive, the E-segment in the second segment, followed by B and so on until as long as the size of the entire drive will not be distributed. Redundancy provides a fourth disc. The first segment of the fourth disc contains an amount modulo 2 (Hog) information segments A, B and C, the first three discs. The next segment of the fourth disc contains Xor (D, E, F), etc. When reading data segment is defined physical address on the disk containing the data. Then read data from all disks simultaneously. When recording also made a request for the display of physical addresses, and recordable data simultaneously posted on all drives. In the process of recording Xor value is calculated for all traffic, and the result has also written to the disk simultaneously. With disk failure data on it can be restored to data from the healthy Hog-diska and the remaining disks. RAID-3 differs from RAID-1 so that the segment size is selected taking into account the mechanism of redundancy. During the operations, or read-write with a crashed disk requires that vssegda Hog-segmentov calculation was possible. For this segment, the size should be small compared to the size of the request that all segments involved in the operation were available in the Hog each time. The typical size segment in RAID-3 a bit or a byte. The request, distributed to all disks, means that every disc will use its portion of the information on request at the same time as drutimi. This ensures a very high speed exchange for large requests, but limited by the number of requests serviced at the same time, because every time you can serve only one request. This provides good performance for load, which is a consistent flow of high demand. RAID-3 provides a good data integrity, since the loss of data is possible only if down another drive will be available before the first refused to be replaced. RAID-2 is very similar to RAID- Z, but instead of a surplus Hog-diska he uses several, which is formed Hamming code and redundant storage inforatsii require some additional disks instead of one. Redundancy can be more expensive.
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