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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