linux磁盘管理软RAID的实现原理分析和方法分享

1 什么是raid

raid全称是独立磁盘冗余阵列（redundant array of independent disks），基本思想是把多个磁盘组合起来，组合一个磁盘阵列组，使得性能大幅提高。

raid分为几个不同的等级，各个不同的等级均在数据可靠性及读写性能做了不同的权衡。实际工作中根据自己的业务需求选择不同的raid方案。

2 raid的实现方式

外接式磁盘阵列：通过扩展卡提供适配能力内接式raid：主板集成raid控制器安装os前在bios里配置软件raid：通过os实现

3 标准的raid

3.1 raid0

raid0称为条带化存储，将数据分段存储在各个磁盘中，读写均可以并行处理，因此读写速率为单个磁盘的n倍，没有冗余功能，任何一个磁盘的损坏就会导致的数据不可用。

3.2 raid1

radi1是镜像存储，没有数据校验，数据被同等的写入到2个或者多个磁盘中，写入速度相对慢， 但是读取速度比较快。

3.3 raid 4

radi4在raid1的基础上，n个盘用于数据存储，另外加入了1个磁盘作为校验盘。一共n+1个盘，任何一个盘坏掉也不影响数据的访问

3.4 raid 5

raid5在raid4的基础上，由原来的一个盘来存储校验数据，改为每个盘都有数据和校验信息的。

4 混合raid

4.1 raid01

先组成raid0,然后组成raid1.

4.2 raid10

先组成raid1,然后组成raid0

5 软raid的实现

5.1 raid5的实现

创建由三块硬盘组成的可用空间为2g的raid5设备，要求其chunk大小为256k，文件系统为ext4，开机可自动挂载至/mydata目录

5.1.1 先看看我们的磁盘情况

[root@centos7 bash]$ lsblk
name maj:min rm size ro type mountpoint
sda 8:0 0 200g 0 disk 
├─sda1 8:1 0 1g 0 part /boot
├─sda2 8:2 0 128g 0 part 
├─sda3 8:3 0 48.8g 0 part /
├─sda4 8:4 0 512b 0 part 
└─sda5 8:5 0 19.5g 0 part /app
sdb 8:16 0 100g 0 disk 
sdc 8:32 0 20g 0 disk 
sdd 8:48 0 20g 0 disk 
sde 8:64 0 20g 0 disk 
sdf 8:80 0 20g 0 disk 
sr0 11:0 1 8.1g 0 rom /run/media/root/centos 7 x86_64　

这里我们使用sdb,sdc,sdd,每个盘创建一个主分区1g,构建radi5.

5.1.2 根据实际情况分区

[root@centos7 bash]$ fdisk /dev/sdb
welcome to fdisk (util-linux 2.23.2).

changes will remain in memory only, until you decide to write them.
be careful before using the write command.

device does not contain a recognized partition table
building a new dos disklabel with disk identifier 0x93d380cf.

command (m for help): n
partition type:
 p primary (0 primary, 0 extended, 4 free)
 e extended
select (default p): p
partition number (1-4, default 1): 
first sector (2048-209715199, default 2048): 
using default value 2048
last sector, +sectors or +size{k,m,g} (2048-209715199, default 209715199): +1g
partition 1 of type linux and of size 1 gib is set

command (m for help): t
selected partition 1
hex code (type l to list all codes): fd
changed type of partition 'linux' to 'linux raid autodetect'

command (m for help): p

disk /dev/sdb: 107.4 gb, 107374182400 bytes, 209715200 sectors
units = sectors of 1 * 512 = 512 bytes
sector size (logical/physical): 512 bytes / 512 bytes
i/o size (minimum/optimal): 512 bytes / 512 bytes
disk label type: dos
disk identifier: 0x93d380cf

 device boot start  end blocks id system
/dev/sdb1  2048 2099199 1048576 fd linux raid autodetect

command (m for help): w
the partition table has been altered!

calling ioctl() to re-read partition table.
syncing disks.
[root@centos7 bash]$ fdisk /dev/sdc
welcome to fdisk (util-linux 2.23.2).

changes will remain in memory only, until you decide to write them.
be careful before using the write command.

device does not contain a recognized partition table
building a new dos disklabel with disk identifier 0xc56b90d8.

command (m for help): n
partition type:
 p primary (0 primary, 0 extended, 4 free)
 e extended
select (default p): p
partition number (1-4, default 1): 
first sector (2048-41943039, default 2048): 
using default value 2048
last sector, +sectors or +size{k,m,g} (2048-41943039, default 41943039): +1g
partition 1 of type linux and of size 1 gib is set

command (m for help): t
selected partition 1
hex code (type l to list all codes): fd
changed type of partition 'linux' to 'linux raid autodetect'

command (m for help): p

disk /dev/sdc: 21.5 gb, 21474836480 bytes, 41943040 sectors
units = sectors of 1 * 512 = 512 bytes
sector size (logical/physical): 512 bytes / 512 bytes
i/o size (minimum/optimal): 512 bytes / 512 bytes
disk label type: dos
disk identifier: 0xc56b90d8

 device boot start  end blocks id system
/dev/sdc1  2048 2099199 1048576 fd linux raid autodetect

command (m for help): w
the partition table has been altered!

calling ioctl() to re-read partition table.
syncing disks.
[root@centos7 bash]$ fdisk /dev/sdd
welcome to fdisk (util-linux 2.23.2).

changes will remain in memory only, until you decide to write them.
be careful before using the write command.

device does not contain a recognized partition table
building a new dos disklabel with disk identifier 0x7e0900d8.

command (m for help): n
partition type:
 p primary (0 primary, 0 extended, 4 free)
 e extended
select (default p): p
partition number (1-4, default 1): 
first sector (2048-41943039, default 2048): 
using default value 2048
last sector, +sectors or +size{k,m,g} (2048-41943039, default 41943039): +1g
partition 1 of type linux and of size 1 gib is set

command (m for help): p

disk /dev/sdd: 21.5 gb, 21474836480 bytes, 41943040 sectors
units = sectors of 1 * 512 = 512 bytes
sector size (logical/physical): 512 bytes / 512 bytes
i/o size (minimum/optimal): 512 bytes / 512 bytes
disk label type: dos
disk identifier: 0x7e0900d8

 device boot start  end blocks id system
/dev/sdd1  2048 2099199 1048576 83 linux

command (m for help): t
selected partition 1
hex code (type l to list all codes): fd
changed type of partition 'linux' to 'linux raid autodetect'

command (m for help): w
the partition table has been altered!

calling ioctl() to re-read partition table.
syncing disks.

5.1.3 创建raid

[root@centos7 bash]$ mdadm -c /dev/md5 -a yes -l 5 -n 3 /dev/sd{b1,c1,d1} -c 256 # -c指定创建， -a yes 自动创建设备 ， -l 设定level , -n 设定磁盘个数， -c chunk大小
continue creating array? y
mdadm: defaulting to version 1.2 metadata
mdadm: array /dev/md5 started.
[root@centos7 bash]$ mdadm -ds        # 查看信息
array /dev/md5 metadata=1.2 name=centos7.magedu.com:5 uuid=2c8ae60d:a799fcb7:9008a046:ae6ea430
[root@centos7 bash]$ mdadm -ds >/etc/mdadm.conf      # 将软raid信息写入到配置文件中去
[root@centos7 bash]$ mkdir /mnt/md5       # 创建挂载点目录 
[root@centos7 bash]$ mkfs.ext4 /dev/md5       # 创建文件系统
mke2fs 1.42.9 (28-dec-2013)
filesystem label=
os type: linux
block size=4096 (log=2)
fragment size=4096 (log=2)
stride=64 blocks, stripe width=128 blocks
131072 inodes, 523776 blocks
26188 blocks (5.00%) reserved for the super user
first data block=0
maximum filesystem blocks=536870912
16 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
superblock backups stored on blocks: 
32768, 98304, 163840, 229376, 294912

allocating group tables: done    
writing inode tables: done    
creating journal (8192 blocks): done
writing superblocks and filesystem accounting information: done 

[root@centos7 bash]$ mount /dev/md5 /mnt/md5      # 挂载设备 
[root@centos7 bash]$ tail -n 1 /etc/mtab
/dev/md5 /mnt/md5 ext4 rw,seclabel,relatime,stripe=128,data=ordered 0 0  # 查看挂载信息
[root@centos7 bash]$ tail -n 1 /etc/mtab >>/etc/fstab     #添加到fstab文件中，确保开机启动，这里建议使用uuid

5.1.4 验证raid

[root@centos7 md5]$ mdadm -d /dev/md5       #查看详细raid5详细信息，可以发现有3个都是working状态的
/dev/md5:
version : 1.2
creation time : wed dec 6 19:28:22 2017
raid level : raid5
array size : 2095104 (2046.00 mib 2145.39 mb)
used dev size : 1047552 (1023.00 mib 1072.69 mb)
raid devices : 3
total devices : 3
persistence : superblock is persistent

update time : wed dec 6 19:39:06 2017
state : clean 
active devices : 3
working devices : 3
failed devices : 0
spare devices : 0

layout : left-symmetric
chunk size : 256k

consistency policy : resync
name : centos7.magedu.com:5 (local to host centos7.magedu.com)
uuid : 2c8ae60d:a799fcb7:9008a046:ae6ea430
events : 18

number major minor raiddevice state
 0 8 17 0 active sync /dev/sdb1
 1 8 33 1 active sync /dev/sdc1
 3 8 49 2 active sync /dev/sdd1
[root@centos7 md5]$ man mdadm
[root@centos7 md5]$ mdadm /dev/md5 -f /dev/sdc1       # -f 设定指定设备故障， 将/dev/sdc1 这个盘标记失败， 看是否数据能访问，我这里使用-f标记失败，工作中可以根据硬盘指示灯判断磁盘状态
mdadm: set /dev/sdc1 faulty in /dev/md5  
[root@centos7 md5]$ mdadm -d /dev/md5        #在次查看信息，发现工作的是2个， 一个失败的设备 
/dev/md5:
version : 1.2
creation time : wed dec 6 19:28:22 2017
raid level : raid5
array size : 2095104 (2046.00 mib 2145.39 mb)
used dev size : 1047552 (1023.00 mib 1072.69 mb)
raid devices : 3
total devices : 3
persistence : superblock is persistent

update time : wed dec 6 19:41:08 2017
state : clean, degraded        # 这里注意了。 我们的一个盘坏掉了。 raid5状态为降级使用了。
active devices : 2
working devices : 2
failed devices : 1
spare devices : 0

layout : left-symmetric
chunk size : 256k

consistency policy : resync
name : centos7.magedu.com:5 (local to host centos7.magedu.com)
uuid : 2c8ae60d:a799fcb7:9008a046:ae6ea430
events : 20

number major minor raiddevice state
0 8 17 0 active sync /dev/sdb1
- 0 0 1 removed
3 8 49 2 active sync /dev/sdd1
1 8 33 - faulty /dev/sdc1
[root@centos7 md5]$ cat a.txt      # 发现我们的数据还是能访问的。没有问题。

5.1.5 替换设备

我这里是磁盘坏掉后的执行替换的， 完全可以多一个备用盘， 坏掉自动替换的。

[root@centos7 md5]$ mdadm /dev/md5 -a /dev/sde1   # 上面我们的sdc1数据损坏，我们需要更换新的磁盘来顶替他的位置。这里添加一个sde1的磁盘， fdisk操作这里省去了。
mdadm: added /dev/sde1
[root@centos7 md5]$ mdadm -ds      # 查看详细信息
array /dev/md5 metadata=1.2 name=centos7.magedu.com:5 uuid=2c8ae60d:a799fcb7:9008a046:ae6ea430
[root@centos7 md5]$ mdadm -d /dev/md5     # 查看详细信息
/dev/md5:
version : 1.2
creation time : wed dec 6 19:28:22 2017
raid level : raid5
array size : 2095104 (2046.00 mib 2145.39 mb)
used dev size : 1047552 (1023.00 mib 1072.69 mb)
raid devices : 3
total devices : 4
persistence : superblock is persistent

update time : wed dec 6 19:50:01 2017
state : clean       # 状态恢复正常了。没有问题
active devices : 3
working devices : 3
failed devices : 1
spare devices : 0

layout : left-symmetric
chunk size : 256k

consistency policy : resync
name : centos7.magedu.com:5 (local to host centos7.magedu.com)
uuid : 2c8ae60d:a799fcb7:9008a046:ae6ea430
events : 43

number major minor raiddevice state
0 8 17 0 active sync /dev/sdb1
4 8 65 1 active sync /dev/sde1
3 8 49 2 active sync /dev/sdd1

1 8 33 - faulty /dev/sdc1  # 这个盘是坏掉的，我们已经加入了新的磁盘， 这个盘可以干掉了
[root@centos7 md5]$ man mdadm
[root@centos7 md5]$ mdadm /dev/md5 --remove /dev/sdc1   # 这个盘我们从raid5中移除去。 
mdadm: hot removed /dev/sdc1 from /dev/md5

5.1.6扩展raid

我们上面使用的是2+1构成的raid5,磁盘利用率为66%，如果我们想改成3+1 可以执行类似如下命令

[root@centos7 mnt]$ mkadm -g -r /dev/md5 -n 4 -a /dev/sdxx   # 这里我就不测试了。使用/dev/sdxx代替一个设备。-g 是grown增长的意思，-r 是resizefs的意思，

5.1.7 清空raid信息

[root@centos7 mnt]$ umount /dev/md5     # 卸载设备
[root@centos7 mnt]$ mdadm -s /dev/md5     # 停止raid5 
mdadm: stopped /dev/md5
[root@centos7 mnt]$ sed -i '$d' /etc/fstab    # 删除fstab中关于raid5挂载的行
[root@centos7 mnt]$ cat /etc/fstab     # 确保fstab没有大问题

#
# /etc/fstab
# created by anaconda on tue nov 7 16:07:01 2017
#
# accessible filesystems, by reference, are maintained under '/dev/disk'
# see man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#

uuid=59ccea87-3c4e-4bbc-9e2f-3fadb1dcf2e6 /   ext4 defaults 1 1
uuid=f4e867e8-bcde-43a2-adc7-c80b0948e85f /app   ext4 noatime,usrquota,grpquota 1 2
uuid=1d6cbe88-ffb4-4adf-bacf-76be1fa75708 /boot   ext4 defaults 1 2
#uuid=b2c064f5-1ee5-4b5c-9e75-ed41cb99c5aa swap   swap defaults 0 0
#uuid=a0516c4f-40e6-4919-905a-8b44db12ff7b swap  swap defaults,pri=0 0 0 
#/dev/sdb2 /test ext4 rw,seclabel,relatime,data=ordered 0 0
#/dev/sdb1 /home xfs rw,seclabel,relatime,attr2,inode64,usrquota,grpquota 0 0
[root@centos7 mnt]$ rm -rf /etc/mdadm.conf     # 删除raid默认配置文件

[root@centos7 mnt]$ mdadm --zero-superblock /dev/sd{b1,e1,d1,c1}  # 清空设置上的超级块信息

5.2 raid10的实现

raid10 ，6个分区，2个一组raid1,3组raid0

5.2.1 案例分析

分析下，我们创建一个raid10设置，2个设备组成一个raid1,6个设备2个一组可以组成3个raid1, 然后把3个raid1组成一个raid0即可

5.2.2 先创建6个设备

[root@centos7 mnt]$ lsblk    # 就是使用fdisk 创建的设备， 具体这里就不写了。 最终使用lsblk显示，我们可以看到sdb1,sdb2,sdd1,sde1一共6个磁盘
name maj:min rm size ro type mountpoint
sda 8:0 0 200g 0 disk 
├─sda1 8:1 0 1g 0 part /boot
├─sda2 8:2 0 128g 0 part 
├─sda3 8:3 0 48.8g 0 part /
├─sda4 8:4 0 512b 0 part 
└─sda5 8:5 0 19.5g 0 part /app
sdb 8:16 0 100g 0 disk 
├─sdb1 8:17 0 1g 0 part 
└─sdb2 8:18 0 1g 0 part 
sdc 8:32 0 20g 0 disk 
├─sdc1 8:33 0 1g 0 part 
└─sdc2 8:34 0 1g 0 part 
sdd 8:48 0 20g 0 disk 
└─sdd1 8:49 0 1g 0 part 
sde 8:64 0 20g 0 disk 
└─sde1 8:65 0 1g 0 part 
sdf 8:80 0 20g 0 disk 
sr0 11:0 1 8.1g 0 rom /run/media/root/centos 7 x86_64

5.2.3 创建raid

[root@centos7 mnt]$ mdadm -c /dev/md11 -a yes -l 1 -n 2 /dev/sd{b1,c1}    # 创建第一个raid1
mdadm: /dev/sdb1 appears to be part of a raid array:
 level=raid5 devices=3 ctime=wed dec 6 19:28:22 2017
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
mdadm: /dev/sdc1 appears to be part of a raid array:
 level=raid5 devices=3 ctime=wed dec 6 19:28:22 2017
continue creating array? y
mdadm: defaulting to version 1.2 metadata
mdadm: array /dev/md11 started.
[root@centos7 mnt]$ mdadm -c /dev/md12 -a yes -l 1 -n 2 /dev/sd{b2,c2}    #创建第二个raid1
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/md12 started.
[root@centos7 mnt]$ mdadm -c /dev/md13 -a yes -l 1 -n 2 /dev/sd{d1,e1}     # 创建第三个raid1
mdadm: /dev/sdd1 appears to be part of a raid array:
level=raid5 devices=3 ctime=wed dec 6 19:28:22 2017
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
mdadm: /dev/sde1 appears to be part of a raid array:
level=raid5 devices=3 ctime=wed dec 6 19:28:22 2017
continue creating array? y
mdadm: defaulting to version 1.2 metadata
mdadm: array /dev/md13 started.
[root@centos7 mnt]$ mdadm -c /dev/md10 -a yes -l 0 -n 3 /dev/md{11,12,13}    # 将3个raid1 合并为一个raid0 
mdadm: /dev/md11 appears to contain an ext2fs file system
size=2095104k mtime=wed dec 6 19:29:45 2017
mdadm: /dev/md13 appears to contain an ext2fs file system
size=2095104k mtime=wed dec 6 19:29:45 2017
continue creating array? y
mdadm: defaulting to version 1.2 metadata
mdadm: array /dev/md10 started.
[root@centos7 mnt]$ mkfs.ext
mkfs.ext2 mkfs.ext3 mkfs.ext4  
[root@centos7 mnt]$ mkfs.ext4 /dev/md10         # 创建文件系统            
mke2fs 1.42.9 (28-dec-2013)
filesystem label=
os type: linux
block size=4096 (log=2)
fragment size=4096 (log=2)
stride=128 blocks, stripe width=384 blocks
196224 inodes, 784896 blocks
39244 blocks (5.00%) reserved for the super user
first data block=0
maximum filesystem blocks=805306368
24 block groups
32768 blocks per group, 32768 fragments per group
8176 inodes per group
superblock backups stored on blocks: 
32768, 98304, 163840, 229376, 294912

allocating group tables: done    
writing inode tables: done    
creating journal (16384 blocks): done
writing superblocks and filesystem accounting information: done 

[root@centos7 mnt]$ mdadm -ds          # 查看配置信息
array /dev/md11 metadata=1.2 name=centos7.magedu.com:11 uuid=0ce2cd6c:cd21fab6:3e65cfb5:64bd86f3
array /dev/md12 metadata=1.2 name=centos7.magedu.com:12 uuid=8af31dff:efab06ed:48e2613b:a599c774
array /dev/md13 metadata=1.2 name=centos7.magedu.com:13 uuid=a8c99d60:2d0c61e7:97a76809:9396c020
array /dev/md10 metadata=1.2 name=centos7.magedu.com:10 uuid=50b2fa58:4ce65d67:8c50c853:fa175a28
[root@centos7 mnt]$ mdadm -ds >> /etc/mdadm.conf        # 写配置文件到mdadm的配置文件中
[root@centos7 mnt]$ mkdir /mnt/md10         # 创建挂载目录
[root@centos7 mnt]$ mount /dev/md10 /mnt/md10        # 挂载文件系统
[root@centos7 mnt]$ tail -n 1 /etc/mtab         # 查看mtab文件中的最后一行， 也就是我们的md10挂载信息
/dev/md10 /mnt/md10 ext4 rw,seclabel,relatime,stripe=384,data=ordered 0 0
[root@centos7 mnt]$ tail -n 1 /etc/mtab >> /etc/fstab       #添加到开机启动

5.2.4 raid 清除工作

[root@centos7 mnt]$ umount /dev/md10         # 取消挂载
[root@centos7 mnt]$ rm -rf /etc/mdadm.conf        # 删除mdadm的默认配置
[root@centos7 mnt]$ mdadm -s /dev/md10         # 停止raid0设置
mdadm: stopped /dev/md10
[root@centos7 mnt]$ mdadm -s /dev/md11         # 停止raid1设置
mdadm: stopped /dev/md11
[root@centos7 mnt]$ mdadm -s /dev/md12         # 停止radi1 设置
mdadm: stopped /dev/md12 
[root@centos7 mnt]$ mdadm -s /dev/md13         # 停止raid 1 设置
mdadm: stopped /dev/md13
[root@centos7 mnt]$ sed -i '$d' /etc/fstab        # 删除fstab的挂载 
[root@centos7 mnt]$ cat /etc/fstab         # 确保正确

#
# /etc/fstab
# created by anaconda on tue nov 7 16:07:01 2017
#
# accessible filesystems, by reference, are maintained under '/dev/disk'
# see man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#

uuid=59ccea87-3c4e-4bbc-9e2f-3fadb1dcf2e6 /   ext4 defaults 1 1
uuid=f4e867e8-bcde-43a2-adc7-c80b0948e85f /app   ext4 noatime,usrquota,grpquota 1 2
uuid=1d6cbe88-ffb4-4adf-bacf-76be1fa75708 /boot   ext4 defaults 1 2
#uuid=b2c064f5-1ee5-4b5c-9e75-ed41cb99c5aa swap   swap defaults 0 0
#uuid=a0516c4f-40e6-4919-905a-8b44db12ff7b swap  swap defaults,pri=0 0 0 
#/dev/sdb2 /test ext4 rw,seclabel,relatime,data=ordered 0 0
#/dev/sdb1 /home xfs rw,seclabel,relatime,attr2,inode64,usrquota,grpquota 0 0
[root@centos7 mnt]$ mdadm -d           # 再次查看下mdadm信息，确保没有了
mdadm: no devices given.
[root@centos7 mnt]$ mdadm --zero-superblock /dev/sd{b1,b2,c1,c2,d1,e1}     # 请求md的元数据信息

以上就是我们给大家整理的在linux磁盘管理中实现软raid的方法讲解，大家有不明白的可以在下方的留言区讨论。