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Contemporary disc systems of RAID

RAID-1. The technology, which is based on the configuration of RAID-1, known for long and named "mirror disks." As before, a user array is a virtual disk device with the necessary amount of memory, broken into segments. These are placed in the same way as traditional disk tonnes. E. segments A, B, C, ... located in the natural order of the first disk. When the disk is full, the data posted in the same way on the third drive, and so on until exhaustion of total memory. Redundancy is achieved by the second disk, which is the exact copy of the first, ie, segments A, B, C, ... there are located in the same places as in the first. Similarly, the fourth disc is an exact copy of the third. Upon receipt of a request for a device to read data can be read from any of the two disks, so that each pair of mirror disks on average performs only half the requests. When recording data written to both disks. If one of the disks fails, access is not interrupted, and no loss of data occurs. All operations performed by the remaining operational disk. Since the location of the data is no different from the traditional, for this configuration there is the problem of "hot spots". A segment is located on the first and second drives, in the next segment, in the third and fourth drives. Segment C located on the first and second drive, followed by A. Segment Segment 0 located on the third and fourth drives next to the segment B, and so on. Dimensions segment chosen large enough in comparison to the size of user queries. If a request is received for reading, access only to those implemented in segments of one of the two disks, which are required data. If this request for the record, the resort also happens only to those segments whose address corresponds to a logical address in the request. The scheme is no longer suffers from the problem of "hot spots", and its performance markedly higher than previously described configuration. Wisdom of the disks "mirror pairs can perform queries on reading at the same time. If you select the segment size smaller than the size of the request, the sequence of requests for large size can be obtained from the performance close to the productivity RAID-0. The workload can be balanced between the discs by selecting the size of the segment in a way that, on average, the best possible performance.
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