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Contemporary disc systems of RAID

RAID-4. Level 4: disks in the array level 4 is not synchronized, as has been done in the disk level 3, and therefore they could work independently, providing a good array of features when using it in multi-file, although the parity continues to inscribe highlighted drive. This is the best solution for file servers, from which users frequently read data, but rarely performed on the record information on disks. RAID-5. The user perceives array as a single logical disk containing the required memory capacity. Restoring data is also provided through Hog operations, but in this case Hog-segmenty distributed to all disks. A segment is located on the first drive, V-segment on the second disc, C-segment in the third drive. The first segment of the fourth disc contains Xor (A, B, C). Segment Data 0 placed on the first drive next to the A segment, a segment on the E-drive followed by the second segment B. The second segment of the third disc, following the C segment contains Xor (D, E, F), and F is the second segment in the fourth drive. For the next three segments Hog (G, H, I) put on the second disc, and so on. The size segment in RAID-5 is also closely related to the mechanism of redundancy. It is expected that during the recording available to only the data needed to calculate the Hog. Used algorithm: Read-Write-changed. A large segment size is selected in relation to the size of the user query. In reading only access to this area on the disk. When the record, the only record this area on the second segment of the disk and related Xor area on the fourth drive. With this amount of the request almost all requests fall inside one segment. When reading data address specified in the request, is shown in a physical address segment on the disk containing the data. Then read data from all disks simultaneously. When recording also made a request to display the physical address, and then read the old data and related Hog-dannye. Recordable data stack modulo 2 with previous Hog-dannymi, the result is a checklist for the amount of new data. New data and new Hog-kombinatsiya written to the appropriate disks.
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