A, RAID disk arrays Introduction
RAID is a Redundant Array of Independent Disks English abbreviation, the Chinese referred to as an independent redundant disk array. A plurality of RAID is to combine separate physical hard in different ways to form a disk group (logical drive), thereby providing a higher performance than a single disk storage data in different ways and provide backup technology called RAID disk array composed levels ( RAID levels), commonly used RAID levels are as follows: RAIDO, RAID1, RAID5, RAID6, RAID1 + 0 and so on.
Two, RAID 0 disk array
RAID 0 consecutive bits or bytes divided data, read and write to multiple disks in parallel, thus having a high data transfer rate, but it has no data redundancy, and therefore can not be considered a RAID configuration. 
RAID 0 is simply to improve performance, and provide no guarantee for the reliability of data, and in which a disk failure will affect all the data. 
RAID 0 can not be used in high data security requirements of the occasion.
Three, RAID 1 disk array
Data redundancy through mirroring disk data, generates data on a mutual backup pair of independent disks. When the original data is busy, data can be read directly from the mirrored copy, so RAID 1 can improve read performance. 
RAID 1 disk array is the highest unit costs, but provides high data security and availability. When a disk fails, the system can automatically switch to the reader the mirror disk failure without data reorganization.
Four, RAID 5 disk array
RAID 5 disk array consists of N (N> = 3) composed of the disk array block, a data generating the N-1 band, as well as a part of check data were N parts iterative equalization data block stored on the N disks. 
N simultaneously read and write disk blocks, high read performance, but because of problems with a checking mechanism, relatively high write performance. Disk capacity of (N-1) / N, high reliability, allowing a bad disk, does not affect any data.
Experimental Analysis:
1, the virtual machine to add four hard disks (each disk 20G) to identify and restart, and then open the terminal performs "fdisk / dev / sdc" command to enter the interactive mode, all in accordance with FIG disk RAID type instruction into steps. 
2, we execute "rpm -q mdadm" command to query whether there mdadm software, no change can be performed "yum install mdadm" command to install (yum repository can refer to specific articles). 
3, the implementation of "mdadm -C -v / dev / md5 -l5 -n3 / dev / sd [bd] 1 -x1 / dev / sde1" command to create a RAID 5 disk array and a reserved as spare. 
4, the implementation of "cat / proc / mdstat" command to view disk synchronization process. 
5, the implementation of "mdadm -D / dev / md5" command to view disk array information. 
6, the implementation of "mdadm -f / dev / md5 / dev / sdb1" command to remove the disk to simulate a disk hung up. 
7, and then perform "mdadm -D / dev / md5" command to view information for a disk array, a bad one can see that the hard disk unattended, spare automatically takes up work. 
(These are the works demonstrate RAID 5 disk array, specifically formatted disk and mount the disk, please refer to chapter)
Five, RAID 6 disk arrays
RAID 6 arrays of N (N> 4) composed of an array of disk blocks, disk capacity of (N-2) / N. Compared with RAID 5, RAD 6 adds a second independent parity block. Two independent parity systems use different algorithms, even if two disks fail concurrently does not affect the use of the data with respect to a greater RAID 5 "write losses, poor writing performance.
The RAID. 6 and substantially the same as the above-described RAID 5 operation, the implementation of "mdadm -C -v / dev / md5 -l5 -n3 / dev / sd [bd] 1 -x1 / dev / sde1" command can be, Remember to keep spare disk, interested friends can try.
Six, RAID 1 + 0 RAID
After RAID 1 + 0 disk array of N (an even number, N> = 4) blocks twenty-two disk image, and then combined into a RAID 0, disk capacity N2. N / 2 blocks disc simultaneously written, N disk blocks read simultaneously, high performance, high reliability.
Experimental Analysis:
1, re-insert the four hard disks (each disk 20G), and made RAID type, and then perform "mdadm -C -v / dev / md01 -l1 -n2 / dev / sd [bc] 1" command to create a first mirror volume, then execute "mdadm -C -v / dev / md02 -l1 -n2 / dev / sd [de] 1" command to create a second mirror volume. 
2, the implementation of "mdadm -C -v / dev / md10 -l0 -n2 / dev / md1 / dev / md2" mirrored volume on the basis of the command to do the composition into two mirrored disk RAID 10 array. 
3, we execute "mdadm -D / dev / md10" command to view information about RAID 10 disk arrays, you can see the capacity of only 40G. 
These are the contents of the RAID 5, RAID 6, RAID 10 in the enterprise use more widely.