mdadm是linux下用于管理软件 RAID 的工具, 可以到这里http://www.cse.unsw.edu.au/~neilb/source/mdadm/下载最新的mdadm源码包
安装：
# tar xvzf mdadm-2.4.tgz
# cd mdadm-2.4
# make
# make install ( or cp -R mdadm /usr/sbin)
基本语法 ： mdadm [mode]
mode 有7种：
Assemble：将以前定义的某个阵列加入当前在用阵列。
Build：Build a legacy array ，每个device 没有 superblocks
Create：创建一个新的阵列，每个device 具有 superblocks
Manage： 管理阵列，比如 add 或 remove
Misc：允许单独对阵列中的某个 device 做操作，比如抹去superblocks 或 终止在用的阵列。
Follow or Monitor:监控 raid 1,4,5,6 和 multipath 的状态
Grow：改变raid 容量或 阵列中的 device 数目
可用的 [options]:
-A, –assemble：加入一个以前定义的阵列
-B, –build：Build a legacy array without superblocks.
-C, –create：创建一个新的阵列
-Q, –query：查看一个device，判断它为一个 md device 或是 一个 md 阵列的一部分
-D, –detail：打印一个或多个 md device 的详细信息
-E, –examine：打印 device 上的 md superblock 的内容
-F, –follow, –monitor：选择 Monitor 模式
-G, –grow：改变在用阵列的大小或形态
-h, –help：帮助信息，用在以上选项后，则显示该选项信息
–help-options
-V, –version
-v, –verbose：显示细节
-b, –brief：较少的细节。用于 –detail 和 –examine 选项
-f, –force
-c, –config= ：指定配置文件，缺省为 /etc/mdadm.conf
-s, –scan：扫描配置文件或 /proc/mdstat以搜寻丢失的信息。配置文件/etc/mdadm.conf
mdadm.conf 格式：
DEVICE 所用到的设备分区列表（在mdadm扫描时，将扫描这些分区）
ARRAY 定义实际的磁盘阵列
简单实例：
DEVICE /dev/sda10 /dev/sda11 /dev/sdb10 /dev/sdb11
ARRAY /dev/md0 devices=/dev/sda11, /dev/sda10
分区：
4.实战RAID
下面将通过实际操作，创建一个RAID1：
4．1 格式化待做软RAID的分区：
准备两个待做RAID1的分区/dev/sda10, /dev/sdb10：
要求： 大小近乎相等，格式为Linux raid autodetect （即：fd）；
# fdisk /dev/sda
The number of cylinders for this disk is set to 9964.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)
Command (m for help): n
Command action
l logical (5 or over)
p primary partition (1-4)
l
First cylinder (1012-9964, default 1012):
Using default value 1012
Last cylinder or +size or +sizeM or +sizeK (1012-1039, default 1012): 1025
Command (m for help): p
Disk /dev/sda: 81.9 GB, 81964302336 bytes
255 heads, 63 sectors/track, 9964 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 1 9964 80035798+ 5 Extended
/dev/sda5 917 927 88326 7 HPFS/NTFS
/dev/sda6 928 996 554211 b Win95 FAT32
/dev/sda7 997 1011 120456 7 HPFS/NTFS
/dev/sda8 1040 9964 71690031 83 Linux
/dev/sda9 1 916 7357707 83 Linux
/dev/sda10 1012 1025 112423+ 83 Linux
Partition table entries are not in disk order
Command (m for help): t (更改分区类型)
Partition number (1-10): 10
Hex code (type L to list codes): fd （分区类型为 Linux raid autodetect）
Command (m for help): w （保存退出）
# fdisk -l /dev/sda
Disk /dev/sda: 81.9 GB, 81964302336 bytes
255 heads, 63 sectors/track, 9964 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 1 9964 80035798+ 5 Extended
/dev/sda5 917 927 88326 7 HPFS/NTFS
/dev/sda6 928 996 554211 b Win95 FAT32
/dev/sda7 997 1011 120456 7 HPFS/NTFS
/dev/sda8 1040 9964 71690031 83 Linux
/dev/sda9 1 916 7357707 83 Linux
/dev/sda10 1012 1025 112423+ fd Linux raid autodetect
Partition table entries are not in disk order
同样创建另一分区/dev/sdb10
＃ fdisk -l /dev/sdb
Disk /dev/sdb: 81.9 GB, 81964302336 bytes
255 heads, 63 sectors/track, 9964 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb2 4501 9964 43889580 5 Extended
/dev/sdb3 667 4500 30796605 83 Linux
/dev/sdb4 658 666 72292+ 83 Linux
/dev/sdb5 5114 5362 2000061 83 Linux
/dev/sdb6 5751 5878 1028128+ 83 Linux
/dev/sdb7 5721 5750 240943+ 83 Linux
/dev/sdb8 5620 5720 811251 83 Linux
/dev/sdb9 6261 9964 29752348+ 83 Linux
/dev/sdb10 4501 4514 112423+ fd Linux raid autodetect
Partition table entries are not in disk order
创建RAID1
＃mdadm -C –verbose /dev/md0 –level=1 –raid-devices=2 /dev/sda10 /dev/sdb10
＃或 mdadm -Cv /dev/md0 -l1 -n2 /dev/sda10 /dev/sdb10
mdadm: chunk size defaults to 64K
mdadm: /dev/sda10 appears to contain an ext2fs file system
size=112320K mtime=Sat Jan 1 06:39:59 2000
mdadm: /dev/sdb10 appears to be part of a raid array:
size=112320K ctime=Sat Jan 1 02:45:14 2000
Continue creating array? y
mdadm: array /dev/md0 started.
＃ mkfs.ext3 /dev/md0 (格式化raid)
mke2fs 1.37 (21-Mar-2005)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
28112 inodes, 112320 blocks
5616 blocks (5.00%) reserved for the super user
First data block=1
14 block groups
8192 blocks per group, 8192 fragments per group
2008 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 23 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
# mdadm -D /dev/md0 （查看raid信息）
/dev/md0:
Version : 00.90.01
Creation Time : Sat Jan 1 02:45:14 2000
Raid Level : raid1
Array Size : 112320 (109.71 MiB 115.02 MB)
Device Size : 112320 (109.71 MiB 115.02 MB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Sat Jan 1 05:08:27 2000
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
UUID : 797b80d8:4b70e2d1:7e427c7e:c9546d1b
Events : 0.10
Number Major Minor RaidDevice State
0 8 10 0 active sync /dev/sda10
1 8 26 1 active sync /dev/sdb10
# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sda10[0] sdb10[1]
112320 blocks [2/2] [UU] raid autodetect
unused devices:
＃ mount /dev/md0 /share/raid （挂载raid）
＃ cp /share/partitionA2 /share/raid
＃ ls /share/raid
lost+found asdf.asf
netatalk.tar
# umount /share/raid
# mdadm /dev/md0 -r /dev/sda10 (将sda10从raid中移除)
# mdadm -D /dev/md0
/dev/md0:
Version : 00.90.01
Creation Time : Sat Jan 1 02:45:14 2000
Raid Level : raid1
Array Size : 112320 (109.71 MiB 115.02 MB)
Device Size : 112320 (109.71 MiB 115.02 MB)
Raid Devices : 2
Total Devices : 1
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Sat Jan 1 05:30:28 2000
State : clean, degraded
Active Devices : 1
Working Devices : 1
Failed Devices : 0
Spare Devices : 0
UUID : 797b80d8:4b70e2d1:7e427c7e:c9546d1b
Events : 0.52
Number Major Minor RaidDevice State
0 0 0 0 removed
1 8 26 1 active sync /dev/sdb10
# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb10[1]
112320 blocks [2/1] [_U]
unused devices:
将sda10的分区类型改为linux (即83)，然后重启，重新挂载，查看分区里的文件：
# fdisk /dev/sda
t–>11 –> 83 –> w
# reboot
# mount /dev/sda10 /share/partition
# ls /share/partition
lost+found asdf.asf
netatalk.tar
和原来作为raid时的内容完全一样，说明raid1 的确是在每个硬盘都写入数据，有较高的可靠性。
4．3 数据恢复：
下面在sda上新建另一分区，sda11，并把它作为raid1的一个分区，即替代原来的sda10；
# mdadm /dev/md0 -a /dev/sda11
mdadm: hot added /dev/sda11
# mdadm -D /dev/md0
/dev/md0:
Version : 00.90.01
Creation Time : Sat Jan 1 02:45:14 2000
Raid Level : raid1
Array Size : 112320 (109.71 MiB 115.02 MB)
Device Size : 112320 (109.71 MiB 115.02 MB)
Raid Devices : 2
Total Devices : 3
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Sat Jan 1 05:50:00 2000
State : clean
Active Devices : 2
Working Devices : 3
Failed Devices : 0
Spare Devices : 1
UUID : 797b80d8:4b70e2d1:7e427c7e:c9546d1b
Events : 0.111
Number Major Minor RaidDevice State
0 8 11 0 active sync /dev/sda11
1 8 26 1 active sync /dev/sdb10
# mount /dev/md0 /share/raid
# ls /share/raid
lost+found asdf.asf
netatalk.tar
4．4 其他操作：
# mdadm -S /dev/md0 （停止raid）
# mdadm -As /dev/md0 （根据mdadm.conf文件启动raid）
# modprobe raid0.ko
# lsmod
raid0 5984 0 – Live 0xbf000000
# mdadm -C –verbose /dev/md0 -l0 -n2 /dev/sda11 /dev/sdb11 (raid0)
# modprobe xor.ko
# modprobe raid5.ko
# lsmod
Module Size Used by Not tainted
raid5 20544 0 – Live 0xbf006000
xor 5544 1 raid5, Live 0xbf003000
raid0 5984 0 – Live 0xbf000000
# mdadm -C –verbose /dev/md0 -l5 -n3 /dev/sda10 /dev/sda11 /dev/sdb11 (raid5)
关于mdadm.conf
echo “DEVICE partitions” > /etc/mdadm.conf bgKLinux联盟
mdadm –detail –scan >> /etc/mdadm.conf
命令使用：
mdadm -Cv /dev/md0 -l1 -n2 /dev/sdb7 /dev/sdb8
mdadm -D /dev/md0
mdadm -S /dev/md0
mdadm -R /dev/md0
mdadm -As (－s指pg mdadm的配置文件，如果没有指定，则使用/etc/mdadm.conf
