raid1 也称为镜像备份。
两块磁盘的数据一模一样。

RAID设备是由两个或多个实际块设备创建的虚拟设备。Linux支持RAID1和其他级别。您需要在两个磁盘上有相同大小的分区，即在第二个磁盘上创建与第一个磁盘完全相同的分区，并将类型设置为fd（Linux raid autodetect）。您需要使用以下命令来创建raid1。

在CentOS Linux中创建软raid1

查看磁盘分区

# fdisk -l
# fdisk -l /dev/sdb
# fdisk -l /dev/sdc

输出示例

Disk /dev/sdb: 73.2 GB, 73295462400 bytes
255 heads, 63 sectors/track, 8910 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1          37      297171      83  Linux

Disk /dev/sdc: 73.2 GB, 73295462400 bytes
255 heads, 63 sectors/track, 8910 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1   *           1          37      297171      83  Linux

修改分区标签

# fdisk /dev/sdb

输出示例：

Command (m for help): p

Disk /dev/sdb: 73.2 GB, 73295462400 bytes
255 heads, 63 sectors/track, 8910 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1          37      297171      83  Linux

Command (m for help): t
Partition number (1-5): 3
Hex code (type L to list codes): fd
Changed system type of partition 3 to fd (Linux raid autodetect)

Command (m for help): p

Disk /dev/sdb: 73.2 GB, 73295462400 bytes
255 heads, 63 sectors/track, 8910 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1          37      297171      fd  Linux

Command (m for help): w
The partition table has been altered!

可以看到id由83变成fd。
同样对sdc进行操作

# fdisk /dev/sdc

重新加载分区

# partprobe /dev/sdb
# partprobe /dev/sdc

或者

# echo 1 > /sys/block/sdb/device/rescan
# echo 1 > /sys/block/sdc/device/rescan

创建raid1阵列

使用/dev/sdb1和/dev/sdc1创建RAID1

# mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1

查看RAID创建进度，

# watch cat /proc/mdstat

在新的软raid设备上创建文件系统

# mkfs.ext3 /dev/md0

mke2fs 1.39 (29-May-2006)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
4872896 inodes, 9737360 blocks
486868 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
298 block groups
32768 blocks per group, 32768 fragments per group
16352 inodes per group
Superblock backups stored on blocks: 
	32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
	4096000, 7962624

Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 39 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

将RAID1挂载到/raid1

执行以下命令：

# mkdir /raid1
# mount /dev/md0 /raid1/
# df -H /raid1/

输出示例：

Filesystem             Size   Used  Avail Use% Mounted on
/dev/md0                40G   185M    38G   1% /raid1

如何测试RAID 1的速度？

可以使用dd命令，如下所示：

使用dd命令一定要注意

# cd /raid1/
# dd if=/dev/zero of=output bs=8k count=256k
# rm output

262144+0 records in
262144+0 records out
2147483648 bytes (2.1 GB) copied, 6.01068 seconds, 357 MB/s

更新/etc/fstab

设置系统启动时，自动挂载软raid文件系统

# echo '/dev/md0 /raid1 ext3 noatime,rw 0 0' >> /etc/fstab

如何获取有关RAID 1的详细信息？

输入以下命令：

# mdadm --query --detail /dev/md0

输出示例：

/dev/md0:
        Version : 0.90
  Creation Time : Wed May 26 01:58:53 2010
     Raid Level : raid1
     Array Size : 38949440 (37.15 GiB 39.88 GB)
  Used Dev Size : 38949440 (37.15 GiB 39.88 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Wed May 26 12:18:22 2010
          State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
  Spare Devices : 0

           UUID : b6f207e1:7f73424f:53f63bfd:e76b77d8
         Events : 0.2

    Number   Major   Minor   RaidDevice State
       0       8        3        0      active sync   /dev/sda3
       1       8       17        1      active sync   /dev/sdb1