RAID(Reduntant Arrays of Independent Disks),即独立冗余磁盘阵列。
RAID的级别：
Raid 0: 条带
Raid 1: 镜像
Raid 2,3,4,5 等校验码类型
Raid 01, Raid 10, Raid 50 等等。
以下是模拟创建RAID1 （2G）的过程：
1、创建raid auto分区(fd)
[root@ant-colonies ~]# fdisk /dev/sda
...
Command (m for help): t
Partition number (1-9): 8
Hex code (type L to list codes): fd
Changed system type of partition 8 to fd (Linux raid autodetect)
...
/dev/sda8 3424 3685 2104483+ fd Linux raid autodetect
/dev/sda9 3686 3947 2104483+ fd Linux raid autodetect
/dev/sda10 3948 4209 2104483+ fd Linux raid autodetect
[root@ant-colonies ~]# partprobe #通知内核重新读取分区信息
[root@ant-colonies ~]# cat /proc/partitions
major minor #blocks name
8 0 125829120 sda
...
8 8 2104483 sda8
8 9 2104483 sda9
8 10 2104483 sda10
2、将磁盘分区做成RAID盘
[root@ant-colonies ~]# mdadm -C /dev/md0 -a yes -l 1 -n 2 /dev/sda{8,9}
mdadm: Note: this array has metadata at the start and
may not be suitable as a boot device. If you plan to
store '/boot' on this device please ensure that
your boot-loader understands md/v1.x metadata, or use
--metadata=0.90
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
[root@ant-colonies ~]# fdisk -l
...
Disk /dev/md0: 2152 MB, 2152857600 bytes
2 heads, 4 sectors/track, 525600 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
[root@ant-colonies ~]# cat /proc/mdstat # 查看RAID信息配置文件
Personalities : [raid1]
md0 : active raid1 sda9[1] sda8[0]
2102400 blocks super 1.2 [2/2] [UU]
unused devices: <none>
[root@ant-colonies ~]# mdadm -D /dev/md0 # 查看RAID的详细信息
/dev/md0:
Version : 1.2
Creation Time : Fri Jan 20 05:29:57 2017
Raid Level : raid1
Array Size : 2102400 (2.01 GiB 2.15 GB)
Used Dev Size : 2102400 (2.01 GiB 2.15 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Fri Jan 20 05:30:08 2017
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Name : ant-colonies:0 (local to host ant-colonies)
UUID : xxxxxxxxxxxxxxxx
Events : 17
Number Major Minor RaidDevice State
0 8 8 0 active sync /dev/sda8
1 8 9 1 active sync /dev/sda9
3、格式化RAID
[root@ant-colonies ~]# mke2fs -j -E stride=16 /dev/md0
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=16 blocks, Stripe width=0 blocks
131648 inodes, 525600 blocks
26280 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=541065216
17 block groups
32768 blocks per group, 32768 fragments per group
7744 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912
Writing inode tables: done
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 30 mounts or 180 days, whichever comes first. Use tune2fs -c or -i to override.
4、模拟磁盘损坏
[root@ant-colonies ~]# mdadm /dev/md0 -f /dev/sda8
mdadm: set /dev/sda8 faulty in /dev/md0
[root@ant-colonies ~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda9[1] sda8[0](F)
2102400 blocks super 1.2 [2/1] [_U]
unused devices: <none>
[root@ant-colonies ~]# mdadm --detail /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Fri Jan 20 05:29:57 2017
Raid Level : raid1
Array Size : 2102400 (2.01 GiB 2.15 GB)
Used Dev Size : 2102400 (2.01 GiB 2.15 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Fri Jan 20 05:55:52 2017
State : clean, degraded
Active Devices : 1
Working Devices : 1
Failed Devices : 1
Spare Devices : 0
Name : ant-colonies:0 (local to host ant-colonies)
UUID : xxxxxxxxxxxxxxxx
Events : 19
Number Major Minor RaidDevice State
0 0 0 0 removed
1 8 9 1 active sync /dev/sda9
0 8 8 - faulty /dev/sda8
5、移除损坏盘
[root@ant-colonies ~]# mdadm /dev/md0 -r /dev/sda8
mdadm: hot removed /dev/sda8 from /dev/md0
[root@ant-colonies ~]# mdadm -D /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Fri Jan 20 05:29:57 2017
Raid Level : raid1
Array Size : 2102400 (2.01 GiB 2.15 GB)
Used Dev Size : 2102400 (2.01 GiB 2.15 GB)
Raid Devices : 2
Total Devices : 1
Persistence : Superblock is persistent
Update Time : Fri Jan 20 06:02:20 2017
State : clean, degraded
Active Devices : 1
Working Devices : 1
Failed Devices : 0
Spare Devices : 0
Name : ant-colonies:0 (local to host ant-colonies)
UUID : 7e24b602:766c7d33:85e03d1a:868c3d08
Events : 20
Number Major Minor RaidDevice State
0 0 0 0 removed
1 8 9 1 active sync /dev/sda9
[root@ant-colonies ~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda9[1]
2102400 blocks super 1.2 [2/1] [_U]
unused devices: <none>
6、添加新盘到阵列
[root@ant-colonies ~]# mdadm /dev/md0 -a /dev/sda10 # 不需要重新格式化
mdadm: added /dev/sda10
[root@ant-colonies ~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda10[2] sda9[1]
2102400 blocks super 1.2 [2/2] [UU]
unused devices: <none>
7、增加热备盘
[root@ant-colonies ~]# mdadm /dev/md0 -a /dev/sda8
mdadm: added /dev/sda8
[root@ant-colonies ~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda8[3](S) sda10[2] sda9[1]
2102400 blocks super 1.2 [2/2] [UU]
unused devices: <none>
[root@ant-colonies ~]# mdadm -D /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Fri Jan 20 05:29:57 2017
Raid Level : raid1
Array Size : 2102400 (2.01 GiB 2.15 GB)
Used Dev Size : 2102400 (2.01 GiB 2.15 GB)
Raid Devices : 2
Total Devices : 3
Persistence : Superblock is persistent
Update Time : Fri Jan 20 06:11:46 2017
State : clean
Active Devices : 2
Working Devices : 3
Failed Devices : 0
Spare Devices : 1
Name : ant-colonies:0 (local to host ant-colonies)
UUID : xxxxxxxxxxxxxxxx
Events : 40
Number Major Minor RaidDevice State
2 8 10 0 active sync /dev/sda10
1 8 9 1 active sync /dev/sda9
3 8 8 - spare /dev/sda8
8、停止RAID阵列
[root@ant-colonies ~]# mdadm -S /dev/md0
mdadm: stopped /dev/md0
[root@ant-colonies ~]# cat /proc/mdstat
Personalities : [raid1]
unused devices: <none>
[root@ant-colonies ~]# mdadm -D /dev/md0
mdadm: cannot open /dev/md0: No such file or directory
9、重新启动RAID阵列
[root@ant-colonies ~]# mdadm -A /dev/md0 /dev/sda{9,10,8}
mdadm: /dev/md0 has been started with 2 drives and 1 spare.
[root@ant-colonies ~]# mdadm -D --scan # 查看磁盘阵列的磁盘数据信息
ARRAY /dev/md0 metadata=1.2 name=ant-colonies:0 UID=7e24b602:766c7d33:85e03d1a:868c3d08
[root@ant-colonies ~]# mdadm -D --scan > /etc/mdadm.conf # 将磁盘阵列信息添加到系统配置文件，当阵列重新装配时系统会自动挂载对应的磁盘
[root@ant-colonies ~]# mdadm --stop /dev/md0
mdadm: stopped /dev/md0
[root@ant-colonies ~]# mdadm -A /dev/md0
mdadm: /dev/md0 has been started with 2 drives.
10、模拟RAID阵列一块盘损坏，热备盘自动启用作为镜像
[root@ant-colonies ~]# mdadm /dev/md0 --fail /dev/sda10
mdadm: set /dev/sda10 faulty in /dev/md0
[root@ant-colonies ~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda10[2](F) sda8[3] sda9[1]
2102400 blocks super 1.2 [2/1] [_U]
[===============>.....] recovery = 76.0% (1600000/2102400) finish=0.0min speed=228571K/sec # 显示系统在恢复数据至sda8
unused devices: <none>
[root@ant-colonies ~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda10[2](F) sda8[3] sda9[1]
2102400 blocks super 1.2 [2/2] [UU]
unused devices: <none>
[root@ant-colonies ~]# watch -n 2 `cat /proc/mdstat` # watch每2s执行一次cat，动态查看数据恢复情况
附：
mdadm: 将任何块设备做成RAID
模式化的命令：
创建模式
-C
专用选项：
-l: 级别
-n #: 设备个数
-a {yes|no}: 是否自动为其创建设备文件
-c: CHUNK大小, 2^n，默认为64K
-x #: 指定空闲盘个数
管理模式
--add, --remove, --fail
mdadm /dev/md# --fail /dev/sda7
监控模式
-F
增长模式
-G
装配模式
-A
查看RAID阵列的详细信息
mdadm -D /dev/md#
--detail
停止阵列：
mdadm -S /dev/md#
--stop
watch: 周期性地执行指定命令，并以全屏方式显示结果
-n #：指定周期长度，单位为秒，默认为2
格式： watch -n # 'COMMAND'
将当前RAID信息保存至配置文件，以便以后进行装配：
mdamd -D --scan > /etc/mdadm.conf
mke2fs -j -E stride=16 /dev/md2 // stride=chuncks/blocksizes (指定stride即条带大小)