mdadm命令简介：

mdadm是linux下用于创建和管理软件RAID的命令，是一个模式化命令。

由于现在服务器一般都带有RAID阵列卡，并且RAID阵列卡也很廉价，且由于软件RAID不能用作启动分区、使用CPU实现，降低CPU利用率的自身缺陷，因此在生产环境下并不适用。

但为了学习可模拟了解RAID原理和管理。

1．命令格式：

mdadm [mode] [options]

2．命令功能：

显示每个文件和目录的磁盘使用空间。

3．命令参数：模式化的命令

3.1.创建模式 -C  Create

专用选项：

-l: 级别  raid0,raid1,raid5,raid6,raid10,raid50

-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64Kchunk64K /Block4K = stride16

-x #: 指定空闲盘个数

eg1.mdadm-C /dev/md0 -a yes-l 5 -n 3 /dev/sdb{5,6,7}

3.2.管理模式

-a: --add,

-r:--remove,

-f:--fail

eg2.mdadm /dev/md2 --fail /dev/sda7

3.3.查看RAID阵列的详细信息

-D--detail   eg3.mdadm -D /dev/md2

3.4.停止阵列：

-S--stopeg4. mdadm -S /dev/md0

3.5.监控模式-F  Follow or Monitor

3.6.增长模式-G  Grow：改变raid容量或阵列中的device数目

3.7.装配模式Assemble,Add

-A ：将以前定义的某个阵列加入当前在用阵列。

使用此命令方可自动装配：mdadm -D --scan > /etc/mdadm.conf

4．使用实例：

实例1.使用3个逻辑盘创建一个RAID0分区，一个RAID5分区，热备盘，删除分区。

[root@localhost ~]# fdisk /dev/sdb

Command (m for help): p

Disk /dev/sdb: 17.1 GB, 17179869184 bytes

255 heads, 63 sectors/track, 2088 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot      Start         End      Blocks   Id  System

/dev/sdb1               1         244     1959898+  83  Linux

/dev/sdb2             245         488     1959930   83  Linux

/dev/sdb3             489         732     1959930   83  Linux

/dev/sdb4             733        2088    10892070    5  Extended

/dev/sdb5             733         982     2008093+  fd  Linux raid autodetect

/dev/sdb6             983        1232     2008093+  83  Linux

/dev/sdb7            1233        1482     2008093+  83  Linux

/dev/sdb8            1483        1732     2008093+  83  Linux

Command (m for help): t

Partition number (1-8): 6

Hex code (type L to list codes):fd

Changed system type of partition 6 to fd (Linux raid autodetect)

Command (m for help): t

Partition number (1-8): 7

Hex code (type L to list codes): fd

Changed system type of partition 7 to fd (Linux raid autodetect)

Command (m for help): t

Partition number (1-8): 8

Hex code (type L to list codes): fd

Changed system type of partition 8 to fd (Linux raid autodetect)

Command (m for help): p

Disk /dev/sdb: 17.1 GB, 17179869184 bytes

255 heads, 63 sectors/track, 2088 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot      Start         End      Blocks   Id  System

/dev/sdb1               1         244     1959898+  83  Linux

/dev/sdb2             245         488     1959930   83  Linux

/dev/sdb3             489         732     1959930   83  Linux

/dev/sdb4             733        2088    10892070    5  Extended

/dev/sdb5             733         982     2008093+  fd  Linux raid autodetect

/dev/sdb6             983        1232     2008093+  fd  Linux raid autodetect

/dev/sdb7            1233        1482     2008093+  fd  Linux raid autodetect

/dev/sdb8            1483        1732     2008093+  fd  Linux raid autodetect

Command (m for help): w

The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.

The kernel still uses the old table.

The new table will be used at the next reboot.

Syncing disks.

[root@localhost ~]# partprobe /dev/sdb

[root@localhost ~]# cat/proc/partitions

major minor  #blocks  name

8    16   16777216 sdb

8    17    1959898 sdb1

8    18    1959930 sdb2

8    19    1959930 sdb3

8    20          0 sdb4

8    21    2008093 sdb5

8    22    2008093 sdb6

8    23    2008093 sdb7

8    24    2008093 sdb8

[root@localhost ~]# mdadm -C /dev/md0 -a yes -l 0 -n 3 /dev/sdb{5,6,7}

mdadm: /dev/sdb5 appears to contain an ext2fs file system

size=3919616K  mtime=Tue Apr 19 15:45:33 2016

Continue creating array? (y/n) y              ***确认创建在用条带(-l 0)分区md0

mdadm: array /dev/md0 started.

[root@localhost ~]# cat /proc/mdstat

Personalities : [raid6] [raid5] [raid4] [raid0]

md0 : activeraid0 sdb7[2] sdb6[1] sdb5[0]

6024000 blocks 64k chunks

unused devices:

[root@localhost ~]# mke2fs -j /dev/md0

mke2fs 1.39 (29-May-2006)

Filesystem label=

OS type: Linux

Block size=4096 (log=2)

Fragment size=4096 (log=2)

753664 inodes, 1506000 blocks

75300 blocks (5.00%) reserved for the super user

First data block=0

Maximum filesystem blocks=1543503872

46 block groups

32768 blocks per group, 32768 fragments per group

16384 inodes per group

Superblock backups stored on blocks:

32768, 98304, 163840, 229376, 294912, 819200, 884736

Writing inode tables: done

Creating journal (32768 blocks): done

Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 29 mounts or

180 days, whichever comes first.  Use tune2fs -c or -i to override.

[root@localhost ~]#fdisk  -l

Disk /dev/md0: 6168 MB, 6168576000 bytes

2 heads, 4 sectors/track, 1506000 cylinders

Units = cylinders of 8 * 512 = 4096 bytes

Disk /dev/md0 doesn't contain a valid partition table

[root@localhost ~]#mount  /dev/md0   /mnt/

[root@localhost ~]#ls   /mnt/

lost+found

实例2.删除在用分区

[root@localhost ~]# umount/mnt/

[root@localhost ~]# mdadm -S /dev/md0

mdadm: stopped /dev/md0

[root@localhost ~]#rm /dev/md0

rm: remove block special file `/dev/md0'?y

实例3.确认创建RAID5(-l 5)分区md0

[root@localhost ~]# mdadm -C /dev/md0 -a yes-l 5 -n 3 /dev/sdb{5,6,7}

mdadm: /dev/sdb5 appears to contain an ext2fs file system

size=6024000K  mtime=Wed Nov  2 13:58:51 2016

mdadm: /dev/sdb5 appears to be part of a raid array:

level=raid0 devices=3 ctime=Wed Nov  2 13:38:28 2016

mdadm: /dev/sdb6 appears to be part of a raid array:

level=raid0 devices=3 ctime=Wed Nov  2 13:38:28 2016

mdadm: /dev/sdb7 appears to be part of a raid array:

level=raid0 devices=3 ctime=Wed Nov  2 13:38:28 2016

Continue creating array? y

mdadm: array /dev/md0 started.

[root@localhost ~]# cat /proc/mdstat          ***建立RAID建立中

Personalities : [raid6] [raid5] [raid4] [raid0]

md0 : active raid5 sdb7[3] sdb6[1] sdb5[0]

4016000 blocks level 5, 64k chunk, algorithm 2 [3/2] [UU_]

[==>..................]  recovery = 10.8% (217256/2008000) finish=0.8min speed=36209K/sec

[root@localhost ~]# cat /proc/mdstat               ***建立RAID完成后

Personalities : [raid6] [raid5] [raid4] [raid0]

md0 : active raid5 sdb7[2] sdb6[1] sdb5[0]

4016000 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]

实例4.查看/dev/md0的RAID信息

[root@localhost ~]# mdadm -D /dev/md0

/dev/md0:

Version : 0.90

Creation Time : Wed Nov  2 14:10:43 2016

Raid Level :raid5

Array Size : 4016000 (3.83 GiB 4.11 GB)

Used Dev Size : 2008000 (1961.27 MiB 2056.19 MB)

Raid Devices : 3

Total Devices : 3

Preferred Minor : 0

Persistence : Superblock is persistent

Update Time : Wed Nov  2 14:11:46 2016

State : clean

Active Devices : 3

Working Devices : 3

Failed Devices : 0

Spare Devices : 0

Layout : left-symmetric

Chunk Size : 64K

UUID : 4c9da4ca:a6715458:70702cb1:47eb89e2

Events : 0.2

Number   Major   Minor   RaidDevice State

0       8       21        0      active sync   /dev/sdb5

1       8       22        1      active sync   /dev/sdb6

2       8       23        2      active sync   /dev/sdb7

实例5.在RAID5中加一个热备盘

[root@localhost ~]#mdadm /dev/md0 -a /dev/sdb8

[root@localhost ~]# mdadm -D /dev/md0

Raid Level : raid5

Number   Major   Minor   RaidDevice State

0       8       21        0      active sync   /dev/sdb5

1       8       22        1      active sync   /dev/sdb6

2       8       23        2      active sync   /dev/sdb7

3       8       24        -      spare   /dev/sdb8

实例6.RAID5中模拟损坏/dev/sdb6盘

[root@localhost ~]# mdadm /dev/md0 -f /dev/sdb6

mdadm: set /dev/sdb6 faulty in /dev/md0

[root@localhost ~]#mdadm -D /dev/md0

Number   Major   Minor   RaidDevice State

0       8       21        0      active sync   /dev/sdb5

3       8       24        1    sparerebuilding   /dev/sdb8

2       8       23        2      active sync   /dev/sdb7

4       8       22        -      faulty spare   /dev/sdb6

[root@localhost ~]# mdadm /dev/md0 -r /dev/sdb6    (--remove)

mdadm: hot removed /dev/sdb6

[root@localhost ~]#mdadm -D /dev/md0

Number   Major   Minor   RaidDevice State

0       8       21        0      active sync   /dev/sdb5

1       8       24        1      active sync   /dev/sdb8

2       8       23        2      active sync   /dev/sdb7

实例7.RAID5中直接建热备盘

[root@localhost ~]# mdadm -C /dev/md0 -a yes-l 5 -n 3 -x 1 /dev/sdb{5,6,7,8}

mdadm: /dev/sdb5 appears to contain an ext2fs file system

size=6024000K  mtime=Wed Nov  2 13:58:51 2016

mdadm: /dev/sdb5 appears to be part of a raid array:

level=raid5 devices=3 ctime=Wed Nov  2 14:10:43 2016

mdadm: /dev/sdb6 appears to be part of a raid array:

level=raid5 devices=3 ctime=Wed Nov  2 14:10:43 2016

mdadm: /dev/sdb7 appears to contain an ext2fs file system

size=6024000K  mtime=Wed Nov  2 13:58:51 2016

mdadm: /dev/sdb7 appears to be part of a raid array:

level=raid5 devices=3 ctime=Wed Nov  2 14:10:43 2016

mdadm: /dev/sdb8 appears to be part of a raid array:

level=raid5 devices=3 ctime=Wed Nov  2 14:10:43 2016

Continue creating array? y

mdadm: array /dev/md0 started.

[root@localhost ~]# cat /proc/mdstat

Personalities : [raid6] [raid5] [raid4] [raid0]

md0 : active raid5 sdb7[4] sdb8[3](S) sdb6[1] sdb5[0]

4016000 blocks level 5, 64k chunk, algorithm 2 [3/2] [UU_]

[>....................]  recovery =  4.7% (95608/2008000) finish=0.9min speed=31869K/sec

实例8.将当前RAID信息保存至配置文件以自动装配

[root@localhost ~]# mdadm -D --scan  >  /etc/mdadm.conf

[root@localhost ~]# cat /etc/mdadm.conf

ARRAY /dev/md0 level=raid5 num-devices=3 metadata=0.90 spares=1 UUID=d97ca386:1349206d:89aa5d1e:96d23bd4

实例9.指定条带大小，提升硬盘访问速度

[root@localhost ~]#cat /proc/mdstat       ***chunk64K /Block4K = stride16

Personalities : [raid6] [raid5] [raid4] [raid0]

md0 : active raid5 sdb7[2] sdb8[3](S) sdb6[1] sdb5[0]

4016000 blocks level 5,64kchunk, algorithm 2 [3/3] [UUU]

[root@localhost ~]# mke2fs-j -E stride=16 -b 4096 /dev/md0

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