-A: 装配模式，重新识别此前实现的RAID
			-C：创建模式，创建RAID
			-F：监控模式

			管理模式：-f, -r, -a

		-C: 创建模式中专用选项
			-n #: 用于创建RAID设备的磁盘个数；
			-l #: 级别
			-a yes: 自动为创建的RAID生成设备文件;
			-c Chunk_Size: 

1. 显示指定的软RAID的详细信息
mdadm -D /dev/md#
2. 将/dev/md#中的/dev/some_device手动设置为损坏		
mdadm /dev/md# -f /dev/some_device
3. 新增设备
 mdadm /dev/md# -a /dev/new_device
4. 停止软raid
mdadm -S /dev/md#
5. 重新启用RAID
mdadm -A /dev/md# /dev/DEVICE...
6. mdadm的配置文件/etc/mdadm.conf
7. 阶段性地执行指定的COMMAND
watch [-n #] <COMMAND>:

1. 因为10G空间，而且有一个空闲盘，因此必须要有4块5G的分区，将物理硬盘创建为RAID设备
[root@backup ~]# mdadm -C /dev/md0 -a yes -n 3 -l 5 -x1 /dev/sdb{5..8}
mdadm: Fail create md0 when using /sys/module/md_mod/parameters/new_array
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
[root@backup ~]# cat /proc/mdstat
Personalities : [raid10] [raid6] [raid5] [raid4] 
md0 : active raid5 sdb7[4] sdb8[3](S) sdb6[1] sdb5[0]
      10475520 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/2] [UU_]
      [=======>.............]  recovery = 38.2% (2001792/5237760) finish=0.2min speed=222421K/sec
2. 查看该raid设备
[root@backup ~]# mdadm -D /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Thu Jul 18 05:56:45 2019
        Raid Level : raid5
        Array Size : 10475520 (9.99 GiB 10.73 GB)
     Used Dev Size : 5237760 (5.00 GiB 5.36 GB)
      Raid Devices : 3
     Total Devices : 4
       Persistence : Superblock is persistent

       Update Time : Thu Jul 18 05:57:11 2019
             State : clean 
    Active Devices : 3
   Working Devices : 4
    Failed Devices : 0
     Spare Devices : 1

            Layout : left-symmetric
        Chunk Size : 512K
Consistency Policy : resync

              Name : backup:0  (local to host backup)
              UUID : f22a4a54:6e782a63:2eab48e2:a838a28e
            Events : 18

    Number   Major   Minor   RaidDevice State
       0       8       21        0      active sync   /dev/sdb5
       1       8       22        1      active sync   /dev/sdb6
       4       8       23        2      active sync   /dev/sdb7

       3       8       24        -      spare   /dev/sdb
3. 创建文件系统，并写入/etc/fstab文件
[root@backup ~]# mke2fs -t ext4 /dev/md0
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
OS type: Linux
[root@backup ~]# tune2fs -L raid5 /dev/md0
[root@backup ~]# blkid /dev/md0           
/dev/md0: LABEL="raid5" UUID="770842d3-89cb-40cc-8c96-7cbc8fd2c2b2" TYPE="ext4" 
[root@backup ~]# echo "LABEL=raid5    /backup  ext4    defaults,acl      0 0"  >>/etc/fstab 
4. 测试是否挂载成功
[root@backup ~]# mount -a   
[root@backup ~]# df -h |grep "/backup"
/dev/md0        9.8G   37M  9.2G   1% /backup

[root@backup ~]# mdadm -f /dev/md0 /dev/sdb5
mdadm: set /dev/sdb5 faulty in /dev/md0
[root@backup ~]# mdadm -r /dev/md0 /dev/sdb5
mdadm: hot removed /dev/sdb5 from /dev/md0
更换好故障硬盘后执行
[root@backup ~]# mdadm -a /dev/md0 /dev/sdb5
mdadm: added /dev/sdb5
查看同步进度
[root@backup ~]# watch -n1 ‘cat /proc/mdstat‘
查看MD的状态
[root@backup ~]# mdadm -D /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Thu Jul 18 05:56:45 2019
        Raid Level : raid5
        Array Size : 10475520 (9.99 GiB 10.73 GB)
     Used Dev Size : 5237760 (5.00 GiB 5.36 GB)
      Raid Devices : 3
     Total Devices : 4
       Persistence : Superblock is persistent

mdadm –S /dev/md0
mdadm --zero-superblock /dev/sdb1

 mdadm –A –s /dev/md0 激活
 mdadm –R /dev/md0