1 什么是RAID

RAID全称是独立磁盘冗余阵列（Redundant Array of Independent Disks），基本思想是把多个磁盘组合起来，组合一个磁盘阵列组，使得性能大幅提高。

RAID分为几个不同的等级，各个不同的等级均在数据可靠性及读写性能做了不同的权衡。实际工作中根据自己的业务需求选择不同的RAID方案。

2 RAID的实现方式

外接式磁盘阵列：通过扩展卡提供适配能力内接式RAID：主板集成RAID控制器安装OS前在BIOS里配置软件RAID：通过OS实现

3 标准的RAID

3.1 RAID0

RAID0称为条带化存储，将数据分段存储在各个磁盘中，读写均可以并行处理，因此读写速率为单个磁盘的N倍，没有冗余功能，任何一个磁盘的损坏就会导致的数据不可用。

3.2 RAID1

RADI1是镜像存储，没有数据校验，数据被同等的写入到2个或者多个磁盘中，写入速度相对慢， 但是读取速度比较快。

3.3 RAID 4

RADI4在RAID1的基础上，N个盘用于数据存储，另外加入了1个磁盘作为校验盘。一共N+1个盘，任何一个盘坏掉也不影响数据的访问

3.4 RAID 5

RAID5在RAID4的基础上，由原来的一个盘来存储校验数据，改为每个盘都有数据和校验信息的。

4 混合RAID

4.1 RAID01

先组成RAID0,然后组成RAID1.

4.2 RAID10

先组成RAID1,然后组成RAID0

5 软RAID的实现

5.1 RAID5的实现

创建由三块硬盘组成的可用空间为2G的RAID5设备，要求其chunk大小为256k，文件系统为ext4，开机可自动挂载至/mydata目录

5.1.1 先看看我们的磁盘情况

[root@centos7 Bash]$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 200G 0 disk 
├─sda1 8:1 0 1G 0 part /boot
├─sda2 8:2 0 128G 0 part 
├─sda3 8:3 0 48.8G 0 part /
├─sda4 8:4 0 512B 0 part 
└─sda5 8:5 0 19.5G 0 part /app
sdb 8:16 0 100G 0 disk 
sdc 8:32 0 20G 0 disk 
sdd 8:48 0 20G 0 disk 
sde 8:64 0 20G 0 disk 
sdf 8:80 0 20G 0 disk 
sr0 11:0 1 8.1G 0 rom /run/media/root/CentOS 7 x86_64　

这里我们使用sdb,sdc,sdd,每个盘创建一个主分区1G,构建RADI5.

5.1.2 根据实际情况分区

[root@centos7 Bash]$ fdisk /dev/sdb
Welcome to fdisk (util-linux 2.23.2).

Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table
Building a new DOS disklabel with disk identifier 0x93d380cf.

Command (m for help): n
Partition type:
 p primary (0 primary, 0 extended, 4 free)
 e extended
Select (default p): p
Partition number (1-4, default 1): 
First sector (2048-209715199, default 2048): 
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-209715199, default 209715199): +1G
Partition 1 of type Linux and of size 1 GiB is set

Command (m for help): t
Selected partition 1
Hex code (type L to list all codes): fd
Changed type of partition 'Linux' to 'Linux raid autodetect'

Command (m for help): p

Disk /dev/sdb: 107.4 GB, 107374182400 bytes, 209715200 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x93d380cf

 Device Boot Start  End Blocks Id System
/dev/sdb1  2048 2099199 1048576 fd Linux raid autodetect

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.
[root@centos7 Bash]$ fdisk /dev/sdc
Welcome to fdisk (util-linux 2.23.2).

Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table
Building a new DOS disklabel with disk identifier 0xc56b90d8.

Command (m for help): n
Partition type:
 p primary (0 primary, 0 extended, 4 free)
 e extended
Select (default p): p
Partition number (1-4, default 1): 
First sector (2048-41943039, default 2048): 
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-41943039, default 41943039): +1G
Partition 1 of type Linux and of size 1 GiB is set

Command (m for help): t
Selected partition 1
Hex code (type L to list all codes): fd
Changed type of partition 'Linux' to 'Linux raid autodetect'

Command (m for help): p

Disk /dev/sdc: 21.5 GB, 21474836480 bytes, 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0xc56b90d8

 Device Boot Start  End Blocks Id System
/dev/sdc1  2048 2099199 1048576 fd Linux raid autodetect

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.
[root@centos7 Bash]$ fdisk /dev/sdd
Welcome to fdisk (util-linux 2.23.2).

Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table
Building a new DOS disklabel with disk identifier 0x7e0900d8.

Command (m for help): n
Partition type:
 p primary (0 primary, 0 extended, 4 free)
 e extended
Select (default p): p
Partition number (1-4, default 1): 
First sector (2048-41943039, default 2048): 
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-41943039, default 41943039): +1G
Partition 1 of type Linux and of size 1 GiB is set

Command (m for help): p

Disk /dev/sdd: 21.5 GB, 21474836480 bytes, 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x7e0900d8

 Device Boot Start  End Blocks Id System
/dev/sdd1  2048 2099199 1048576 83 Linux

Command (m for help): t
Selected partition 1
Hex code (type L to list all codes): fd
Changed type of partition 'Linux' to 'Linux raid autodetect'

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.