Linux命令：mdadm

[b]mdadm命[/b]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 --stop eg4. 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 : active raid0 sdb7[2] sdb6[1] sdb5[0]
6024000 blocks 64k chunks
unused devices: <none>

[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 spare rebuilding /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, 64k chunk, algorithm 2 [3/3] [UUU]

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

---end---