RAID 10

和RAID 01相反，RAID10是先做RAID1，再做RAID0，如下图所示：

RAID10和RAID01在读写速度上没有什么太大的差别，但是RAID10的数据安全性比较高，若下图左边那组RAID1中磁盘损坏了一个，另外一个也能用，右边那组RAID1再损坏一个数据也是恢复的，除非一组RAID1中的磁盘都坏掉了。

RAID 10的优缺点：

1)较高的容错能力

2)RAID10需要N个磁盘(N>=4)

RAID 50

RAID 50是RAID5和RAID0的组合，先做RAID5，再做RAID0，RAID 5至少需要3颗硬盘，因此要以多组RAID 5构成RAID 50，至少需要6颗硬盘，如下图。

在底层的任意一组或者多组的RAID5中出现了一个磁盘的损坏是可以接受的，但是若出现了2个或者以上的磁盘损坏，整个RAID50就会损坏。

RAID50的优缺点：

1)较高的容错能力

2)RAID10需要N个磁盘(N>=6)

JBOD

Just a Bunch of Disks，能够将多块磁盘的空间合并起来的一个连续的空间，可靠性较低。

在Linux系统上实现Software RAID

在CentOS中，使用模块化得工具mdadm，如果没有可以使用：

yum -y install mdadm

基本用法如下：

命令的语法格式：mdadm [mode] [options]

-C：创建模式-n #: 使用#个块设备来创建此RAID；-l #：指明要创建的RAID的级别；-a {yes|no}：自动创建目标RAID设备的设备文件；-c CHUNK_SIZE: 指明块大小；-x #: 指明空闲盘的个数；-D：显示raid的详细信息

mdadm-D /dev/md#

管理模式：-f：标记指定磁盘为损坏-a：添加磁盘-r：移除磁盘

停止md设备：

mdadm-S /dev/md#

举例：创建一个可用空间为10G的RAID1设备，文件系统为ext4，有一个空闲盘，开机可自动挂载至/backup目录。

先来分析一下：RAID1为镜像磁盘阵列，最少需要2个磁盘，可用空间为10G，即磁盘最小大小为10G即可，我们这里就使用1块硬盘的不同分区来模拟各个磁盘，每个10G：

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

Disk/dev/sdb: 128.8 GB, 128849018880bytes255 heads, 63 sectors/track, 15665cylinders

Units= cylinders of 16065 * 512 = 8225280bytes

Sector size (logical/physical): 512 bytes / 512bytes

I/O size (minimum/optimal): 512 bytes / 512bytes

Disk identifier:0xf9b59c0fDevice Boot Start End Blocks Id System/dev/sdb1 1 1306 10490413+ 83Linux/dev/sdb2 1307 2612 10490445 83Linux/dev/sdb3 2613 3918 10490445 83 Linux

使用以下命令创建RAID1系统，-C为创建模式，/dev/md0设备文件名，-n 2：使用2个块设备创建此RAID，-x 1：指定1个空闲盘的，-l：指定硬盘RAID等级，-a yes：自动创建RAID的设备文件,/dev/adb{1,2,3}：指定磁盘位置

[root@localhost ~]# mdadm -C /dev/md0 -n 2 -x 1 -l 1 -c 128 -a yes /dev/sdb{1,2,3}

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=0.90Continue creating array?y

mdadm: Defaulting to version1.2metadata

mdadm: array/dev/md0 started.

使用 cat /proc/mdstat 查看RAID构建的进度和预期完成的时间：

unused devices: [root@localhost~]# cat /proc/mdstat

Personalities : [raid1]

md0 : active raid1 sdb3[2](S) sdb2[1] sdb1[0]10482176 blocks super 1.2 [2/2] [UU]

[=============>.......] resync = 68.6% (7200128/10482176) finish=0.2min speed=200001K/sec

unused devices:[root@localhost~]# cat /proc/mdstat

Personalities : [raid1]

md0 : active raid1 sdb3[2](S) sdb2[1] sdb1[0]10482176 blocks super 1.2 [2/2] [UU]

unused devices:

查看RAID1的详情：

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

Version :1.2Creation Time : Sun Jul30 05:16:32 2017Raid Level : raid1

Array Size :10482176 (10.00 GiB 10.73GB)

Used Dev Size :10482176 (10.00 GiB 10.73GB)

Raid Devices :2Total Devices :3Persistence : Superblock is persistent

Update Time : Sun Jul30 05:17:25 2017State : clean

Active Devices :2Working Devices :3Failed Devices :0Spare Devices :1Name : localhost.localdomain:0(local to host localhost.localdomain)

UUID : a46c7642:a46e274a:05923aeb:4c1ae0e9

Events :17Number Major Minor RaidDevice State0 8 17 0 active sync /dev/sdb11 8 18 1 active sync /dev/sdb22 8 19 - spare /dev/sdb3

格式化RAID1为ext4文件系统：

[root@localhost ~]# mkfs.ext4 /dev/md0

mke2fs1.41.12 (17-May-2010)

文件系统标签=操作系统:Linux

块大小=4096 (log=2)

分块大小=4096 (log=2)

Stride=0 blocks, Stripe width=0blocks655360 inodes, 2620544blocks131027 blocks (5.00%) reserved forthe super user

第一个数据块=0Maximum filesystem blocks=2684354560

80 block groups

32768 blocks per group, 32768fragments per group8192inodes per group

Superblock backups stored on blocks:32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632正在写入inode表: 完成

Creating journal (32768blocks): 完成

Writing superblocks and filesystem accounting information: 完成

This filesystem will be automatically checked every35mounts or180 days, whichever comes first. Use tune2fs -c or -i to override.

将/dev/md0挂载到/backup目录下：

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

[root@localhost~]# dfFilesystem 1K-blocks Used Available Use%Mounted on/dev/mapper/VolGroup-lv_root 51606140 1122252 47862448 3% /tmpfs953276 0 953276 0% /dev/shm/dev/sda1 495844 33466 436778 8% /boot/dev/mapper/VolGroup-lv_home 67708512 184084 64085020 1% /home/dev/md0 10317624 154100 9639416 2% /backup

可以使用 -f 将其中的某个磁盘模拟为坏的故障硬盘

[root@localhost backup]# mdadm /dev/md0 -f /dev/sdb1

mdadm: set/dev/sdb1 faulty in /dev/md0

再来看一下RAID1的详细信息，/dev/sdb3状态变为active

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

Version :1.2Creation Time : Sun Jul30 05:16:32 2017Raid Level : raid1

Array Size :10482176 (10.00 GiB 10.73GB)

Used Dev Size :10482176 (10.00 GiB 10.73GB)

Raid Devices :2Total Devices :3Persistence : Superblock is persistent

Update Time : Sun Jul30 05:37:02 2017State : clean

Active Devices :2Working Devices :2Failed Devices :1Spare Devices :0Name : localhost.localdomain:0(local to host localhost.localdomain)

UUID : a46c7642:a46e274a:05923aeb:4c1ae0e9

Events :38Number Major Minor RaidDevice State2 8 19 0 active sync /dev/sdb31 8 18 1 active sync /dev/sdb20 8 17 - faulty /dev/sdb1

使用 -r 选项能够移除坏的硬盘

[root@localhost backup]# mdadm /dev/md0 -r /dev/sdb1

mdadm: hot removed/dev/sdb1 from /dev/md0

好的，我们再来添加一块分区当做磁盘

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

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to

switch off the mode (command 'c') and change display units to

sectors (command'u').

Command (mforhelp): n

Command action

e extended

p primary partition (1-4)

p

Selected partition4First cylinder (3919-15665, default 3919):

Using default value3919Last cylinder,+cylinders or +size{K,M,G} (3919-15665, default 15665): +10G

Command (mfor help): wThe partition table has been altered!Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: 设备或资源忙.

The kernel still uses the old table. The new table will be used at

the next reboot or after you run partprobe(8) or kpartx(8)

咦，有告警！因为当前的磁盘已经有分区被挂载当根文件系统的目录上了，内核没有识别，我们来查看/proc/parttions，果真没有识别

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

major minor #blocks name8 16 125829120sdb8 17 10490413sdb18 18 10490445sdb28 19 10490445sdb38 0 125829120sda8 1 512000sda18 2 125316096sda2253 0 52428800 dm-0

253 1 4096000 dm-1

253 2 68788224 dm-2

9 0 10482176 md0

使用以下命令通知内核强制重读以下磁盘分区表

[root@localhost backup]# partx -a /dev/sdb

添加/dev/sdb4到RAID1

[root@localhost backup]# mdadm /dev/md0 -a /dev/sdb4

mdadm: added/dev/sdb4

查看RAID1的详细信息，/dev/sdb4成功被加入

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

Version :1.2Creation Time : Sun Jul30 05:16:32 2017Raid Level : raid1

Array Size :10482176 (10.00 GiB 10.73GB)

Used Dev Size :10482176 (10.00 GiB 10.73GB)

Raid Devices :2Total Devices :3Persistence : Superblock is persistent

Update Time : Sun Jul30 05:51:52 2017State : clean

Active Devices :2Working Devices :3Failed Devices :0Spare Devices :1Name : localhost.localdomain:0(local to host localhost.localdomain)

UUID : a46c7642:a46e274a:05923aeb:4c1ae0e9

Events :40Number Major Minor RaidDevice State2 8 19 0 active sync /dev/sdb31 8 18 1 active sync /dev/sdb23 8 20 - spare /dev/sdb4

设置开机可以自动挂载只/backup目录下，修改配置文件/etc/fstab即可

#

#/etc/fstab

# Created by anaconda on Fri Jul28 06:34:35 2017#

# Accessible filesystems, by reference, are maintained under'/dev/disk'# Seeman pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info#/dev/mapper/VolGroup-lv_root / ext4 defaults 1 1UUID=bc67ad74-46b3-4abc-b8a7-c4fb7cd6552a /boot ext4 defaults 1 2

/dev/mapper/VolGroup-lv_home /home ext4 defaults 1 2

/dev/mapper/VolGroup-lv_swap swap swap defaults 0 0tmpfs/dev/shm tmpfs defaults 0 0devpts/dev/pts devpts gid=5,mode=620 0 0sysfs/sys sysfs defaults 0 0proc/proc proc defaults 0 0

/dev/md0 /backup ext4 defaults 0 0

小知识点：

在查看RAID创建过程的进度时候，可加上watch命令动态查看创建RAID的进度

watch  [options]  'COMMAND'

选项

-n# ：指定刷新间隔，单位秒

watch -n1 'cat /proc/mdstat'