Linux Learning-disk array raid

disk array-the integration of multiple disks into a larger disk through a certain technology, not only increased capacity, but also the data on the disk has the function of maintenance, recovery, read faster.

RAID has different common levels, so that the consolidated disk has different functions:

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RAID 0 (Isometric mode)

This mode of RAID has the best performance for each disk with the same model and capacity .

: Each disk is divided into the same size chunk block, and each disk chunk block is also equal, when the data is stored, the data is first cut into chunk block size of small data, and then interleaved in the chunk of each disk, So the data stored on each disk is averaged, with 200M of data allocated to 100M of data per disk, which reduces the burden of one disk storing all the data, and the more disk performance the better, thecapacity of the raid is the sum of the capacity of each disk.

When the capacity of each disk is unequal, the initial data is interleaved in each disk chunk, and when the minimum disk space is exhausted, the remaining data is placed on the largest disk.

The performance will become worse.

However, the damage to RAID 0 is still very large, if a disk is broken, then the entire RAID 0 will not be used.

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RAID 1 (Image mode)

The capacity of each disk in RAID 1 is the best, but when the disk capacity is not the same, the smallest disk is the primary.

RAID 1 mode, a full backup of the data to two disks, so that the overall raid capacity will be reduced by 50%.

When data is heavily written to raid, because one copy of the data is backed up multiple times, the efficiency of writing becomes very poor, and the advantage is that when the data of a piece of disk is broken, another piece of backup data will work, enhancing the security of the data.

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RAID 1+0

Combining RAID 0 efficiency with RAID 1 security results in a raid 1+0

Disk 1 and Disk 2 are combined into a set of RAID 1, disk 3 and disk 4 are also combined into a set of RAID 1, and the last two groups of RAID 1 are composed of RAID 0, when 200M data is written to the raid 1+0,

RAID 0 divides the data into 100M, respectively, into two RAID 1, and the RAID 1 allows each disk to back up 100M of data.

This mode has been greatly improved regardless of the data read and write speed and data security .

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RAID 5

This mode requires at least 3 disks to make up such a disk array, which is similar to RAID 0, and is interleaved to write blocks in turn, with each loop writing a check data (partity) on a different disk, which records the backup data of the other disks, when one of the disks is damaged , which can be recovered based on this check data.

As shown, each of the cyclic write processes records a parity, and on different disks, and because of the parity relationship, the capacity of RAID 5 is the total number of disks-1 of the capacity, in the case of 3-1=2 capacity.

Another problem with RAID 5 is that the number of disks allowed to be corrupted is only one , and if the number of disks damaged is greater than or equal to 2, the entire raid fails.

The ability to read data in this mode is very strong, but in the case of writing data, because of the parity relationship, when the data is written to calculate the parity, so the performance of writing data also need to be discussed.

similar to raid 6 and RAID 5, RAID 6 adds two disks as parity writes, so RAID 6 allows a maximum of two disks to be damaged.

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Several common patterns of disk arrays are compared:

Linux Learning-disk array raid