raid是当前存储提高安全和性能的主要技术手段，实现raid一般用raid卡实现，也就是硬raid。除此之外，我们还可以用软件来实现raid技术。

这篇文章就简单介绍如何用软件实现raid技术（以raid0为例）。

有两个可以实现软raid的工具：raidtools, mdadm。

raidtool，这是在RHEL3中所使用的，但是我在RHEL4中没有找到raidtool,只有mdadm，看来RH也是偏向于使用mdadm的。本文也以mdadm为例讲述。

一、查看当前硬盘情况

[root@primary /]# fdisk -l

Disk /dev/sda: 10.7 GB, 10737418240 bytes

255 heads, 63 sectors/track, 1305 cylindersUnits = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System

/dev/sda1 * 1 13 104391 83 Linux/dev/sda2 14 1114 8843782+ 83 Linux/dev/sda3 1115 1305 1534207+ 82 Linux swap

Disk /dev/sdb: 107 MB, 107374080 bytes

64 heads, 32 sectors/track, 102 cylindersUnits = cylinders of 2048 * 512 = 1048576 bytes

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

Disk /dev/sdc: 107 MB, 107374080 bytes

64 heads, 32 sectors/track, 102 cylindersUnits = cylinders of 2048 * 512 = 1048576 bytes

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

二、为硬盘分区

raid一般多个硬盘来组成，你也可以用同一个硬盘的多个分区组成raid，但这样是没有意义的。

[root@primary /]# fdisk /dev/sdb

Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabelBuilding a new DOS disklabel. Changes will remain in memory only,until you decide to write them. After that, of course, the previouscontent won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): n

Command action e extended p primary partition (1-4)pPartition number (1-4): 1First cylinder (1-102, default 1): Using default value 1Last cylinder or +size or +sizeM or +sizeK (1-102, default 102): Using default value 102

Command (m for help): w

The partition table has been altered!

Calling ioctl() to re-read partition table.

Syncing disks.[root@primary /]# fdisk /dev/sdcDevice contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabelBuilding a new DOS disklabel. Changes will remain in memory only,until you decide to write them. After that, of course, the previouscontent won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): n

Command action e extended p primary partition (1-4)pPartition number (1-4): 1First cylinder (1-102, default 1): Using default value 1Last cylinder or +size or +sizeM or +sizeK (1-102, default 102): Using default value 102

Command (m for help): w

The partition table has been altered!

Calling ioctl() to re-read partition table.

Syncing disks.

此时硬盘的分区情况：

[root@primary /]# fdisk -l

Disk /dev/sda: 10.7 GB, 10737418240 bytes

255 heads, 63 sectors/track, 1305 cylindersUnits = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System

/dev/sda1 * 1 13 104391 83 Linux/dev/sda2 14 1114 8843782+ 83 Linux/dev/sda3 1115 1305 1534207+ 82 Linux swap

Disk /dev/sdb: 107 MB, 107374080 bytes

64 heads, 32 sectors/track, 102 cylindersUnits = cylinders of 2048 * 512 = 1048576 bytes

Device Boot Start End Blocks Id System

/dev/sdb1 1 102 104432 83 Linux

Disk /dev/sdc: 107 MB, 107374080 bytes

64 heads, 32 sectors/track, 102 cylindersUnits = cylinders of 2048 * 512 = 1048576 bytes

Device Boot Start End Blocks Id System

/dev/sdc1 1 102 104432 83 Linux

三、创建raid0

[root@primary /]# mdadm --create /dev/md0 --level=raid0 --chunk=8 --raid-devices=2 /dev/sdb1 /dev/sdc1

四、格式化raid

mdadm: array /dev/md0 started.[root@primary /]# mkfs.ext3 /dev/md0mke2fs 1.35 (28-Feb-2004)max_blocks 213647360, rsv_groups = 26080, rsv_gdb = 256Filesystem label=OS type: LinuxBlock size=1024 (log=0)Fragment size=1024 (log=0)52208 inodes, 208640 blocks10432 blocks (5.00%) reserved for the super userFirst data block=1Maximum filesystem blocks=6737100826 block groups8192 blocks per group, 8192 fragments per group2008 inodes per groupSuperblock backups stored on blocks: 8193, 24577, 40961, 57345, 73729, 204801

Writing inode tables: done

inode.i_blocks = 3586, i_size = 67383296Creating journal (4096 blocks): doneWriting superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 26 mounts or

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

五、挂载raid分区

[root@primary /]# mount /dev/md0 /opt[root@primary /]# df -hFilesystem Size Used Avail Use% Mounted on/dev/sda2 8.4G 5.7G 2.3G 73% //dev/sda1 99M 8.4M 86M 9% /bootnone 252M 0 252M 0% /dev/shm/dev/hdc 161M 161M 0 100% /media/cdrom/dev/md0 198M 5.8M 182M 4% /opt

六、查看raid的信息

[root@primary opt]# mdadm --detail /dev/md0/dev/md0: Version : 00.90.01 Creation Time : Sun Jul 8 22:54:28 2007 Raid Level : raid0 Array Size : 208640 (203.75 MiB 213.65 MB) Raid Devices : 2 Total Devices : 2Preferred Minor : 0 Persistence : Superblock is persistent

Update Time : Sun Jul 8 22:54:29 2007

State : cleanActive Devices : 2Working Devices : 2Failed Devices : 0 Spare Devices : 0

Chunk Size : 8K

Number Major Minor RaidDevice State

0 8 17 0 active sync /dev/sdb1 1 8 33 1 active sync /dev/sdc1 UUID : a86f0502:df5715c0:fd871bbc:9f75e0ad Events : 0.1七、生成mdadm配置文件mdadm的缺省配置文件为/etc/mdadm.conf，它主要是为了方便阵列的日常管理而设置的，对于阵列而言不是必须的，但是为了减少日后管理中不必要的麻烦，还是应该坚持把这一步做完。

在mdadm.conf文件中要包含两种类型的行：一种是以DEVICE开头的行，它指明在阵列中的设备列表；另一种是以ARRAY开头的行，它详细地说明了阵列的名称、模式、阵列中活动设备的数目以及设备的UUID号。

我们可以用mdadm -Ds来得到mdadm.conf文件需要的信息： [root@primary ~]# mdadm -DsARRAY /dev/md0 level=raid0 num-devices=2 UUID=63f24968:d367038d:f207e458:9a803df9 devices=/dev/sdb1,/dev/sdc1

根据上面的信息编辑/etc/mdadm.conf，如下：

[root@primary ~]# more /etc/mdadm.conf ARRAY /dev/md0 level=raid0 num-devices=2 UUID=63f24968:d367038d:f207e458:9a803df9device /dev/sdb1 /dev/sdc1

如果不配置这个文件，在重启后尝试mount raid设备的时候会报错：

[root@primary ~]# mount /dev/md0 /opt/dev/md0: Invalid argumentmount: /dev/md0: can't read superblock

八、设置开机自动挂载

为了让系统开机后能自动挂载raid设备，需要在/etc/fstab添加如下行：vi /etc/fstab/dev/md0 /opt ext3 defaults 0 0

至此，一个raid0就算配置完毕了。其他级别的raid也可以用类似的方法配置，具体可以看帮助。

用mdadm创建raid10

raid0 + raid1的也称raid10，它提供了足够的数据安全和性能，是一般企业最常用的raid级别。今天我们讨论如何用mdadm创建软raid10.

本次实验的测试环境是: vmware + linux as4

1、首先在vmware添加四个虚拟SCSI硬盘，作为实验所用硬盘略过。

2、为四个虚拟硬盘分区

略过

3、创建raid

创建raid10的顺序是：先创建2个raid0，再把2个raid0配置成一个raid1.--创建第一个raid0[root@primary ~]# mdadm --create /dev/md0 --level=raid0 --chunk=8 --raid-devices=2 /dev/sdb1 /dev/sdc1mdadm: array /dev/md0 started.--创建第二个raid0[root@primary ~]# mdadm --create /dev/md1 --level=raid0 --chunk=8 --raid-devices=2 /dev/sdd1 /dev/sde1mdadm: array /dev/md1 started.--利用上面的两个raid0创建raid1[root@primary ~]# mdadm --create /dev/md2 --level=raid1 --chunk=8 --raid-devices=2 /dev/md0 /dev/md1mdadm: array /dev/md2 started.

4、格式话raid设备

注意：对于raid设备，只需要格式化最顶层的设备，不管该raid包含了多少层。在本例中，md2是最顶层的设备，因此我们要把它格式化了就可以了。[root@primary ~]# mkfs.ext3 /dev/md2mke2fs 1.35 (28-Feb-2004)max_blocks 213581824, rsv_groups = 26072, rsv_gdb = 256Filesystem label=OS type: LinuxBlock size=1024 (log=0)Fragment size=1024 (log=0)52208 inodes, 208576 blocks10428 blocks (5.00%) reserved for the super userFirst data block=1Maximum filesystem blocks=6737100826 block groups8192 blocks per group, 8192 fragments per group2008 inodes per groupSuperblock backups stored on blocks:8193, 24577, 40961, 57345, 73729, 204801

Writing inode tables: done

inode.i_blocks = 3586, i_size = 67383296Creating journal (4096 blocks): doneWriting superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 21 mounts or

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

5、查看当前raid信息[root@primary opt]# cat /proc/mdstatPersonalities : [raid0] [raid1]md2 : active raid1 md1[1] md0[0]208576 blocks [2/2] [UU]

md1 : active raid0 sde1[1] sdd1[0]

208640 blocks 8k chunks

md0 : active raid0 sdc1[1] sdb1[0]

208640 blocks 8k chunks

unused devices:

6、挂载raid设备

[root@primary ~]# mount /dev/md2 /opt[root@primary ~]# df -hFilesystem Size Used Avail Use% Mounted on/dev/sda2 8.4G 5.8G 2.2G 73% //dev/sda1 99M 8.4M 86M 9% /bootnone 252M 0 252M 0% /dev/shm/dev/md2 198M 5.8M 182M 4% /opt

7、配置/etc/mdadm.conf首先得出raid的信息：[root@primary opt]# mdadm -DsARRAY /dev/md2 level=raid1 num-devices=2 UUID=97e0cb8d:3613c0eb:6d2b2a87:be1c8030devices=/dev/md0,/dev/md1ARRAY /dev/md1 level=raid0 num-devices=2 UUID=634ab4f9:92d40a05:3b6d00ca:d28a2683devices=/dev/sdd1,/dev/sde1ARRAY /dev/md0 level=raid0 num-devices=2 UUID=fe4f0d31:32580633:45d6f507:d0b7d41adevices=/dev/sdb1,/dev/sdc1

然后编辑/etc/mdadm.conf，添加如下内容：

[root@primary opt]# vi /etc/mdadm.conf

ARRAY /dev/md2 level=raid1 num-devices=2 UUID=97e0cb8d:3613c0eb:6d2b2a87:be1c8030

device /dev/md0 /dev/md1ARRAY /dev/md1 level=raid0 num-devices=2 UUID=634ab4f9:92d40a05:3b6d00ca:d28a2683device /dev/sdd1 /dev/sde1ARRAY /dev/md0 level=raid0 num-devices=2 UUID=fe4f0d31:32580633:45d6f507:d0b7d41adevice /dev/sdb1 /dev/sdc1

8、设置开机自动挂载

为了让系统开机后能自动挂载raid设备，需要在/etc/fstab添加如下行：vi /etc/fstab/dev/md2 /opt ext3 defaults 0 0

至此，raid10配置完毕。

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