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Memory for disk arrays

When recording data stream is divided into blocks (straypy) at the byte level (although perhaps at the level of bits), and writes to all disks simultaneously array except for a dedicated storage control information. To calculate the control information (also referred to as control by the amount) is used operation "excluding " OR (XOR) applied to the recorded data block. In any failure of the disk data on it can be restored to control by the data and data on the healthy remaining disks. Let's look at an illustration of the size of the blocks, four bits. Let there were four disk storage and one disk to record amounts of control. If there is a sequence bit 1101001111001011, broken into blocks of four bits, then to calculate 1011 = 1001. 1100 0011 the checksum operation must be met: 1101 Thus, the checklist Sum-1001: Disc 1 Disc 2 Disc Z Disc 4 Disc 5 1101 0011 1100 1011 1001 If one of the disks, for example, third, went down, the 1100 block will be unavailable reading. However, it is easy to restore the value of the control values and the amount of steel-based units, using all the same Block 4 operation "exclusive" OR: Block 3 = Block 1 Block 2 1011 0011 Control amount. In this example, receive: Block 3 = 1101 1001 = 1100. RAID Level 3 is much less redundancy than RAID 2. Because of segmentation data blocks on RAID 3 has a high performance. When reading information is not pro-treatment granted to the disk with checksums (in the absence of failure), which occurs whenever operation. Because every time I / O operation performed educa strike almost all the disk array, simultaneous processing of multiple requests can be impossible. This level is suitable for applications with the files large volume and low frequency applications.
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