Linux RAID卷

1、Raid定义

RAID,全称Redundant Array of Inexpensive Disks,中文名为廉价磁盘冗余阵列.RAID可分为软RAID和硬RAID,软RAID是通过软件实现多块硬盘冗余的.而硬RAID是一般通过RAID卡来实现RAID的.前者配置简单,管理也比较灵活.对于中小企业来说不失为一最佳选择.硬RAID往往花费比较贵.不过,在性能方面具有一定优势.

2、RAID分类

常见的RAID可分为以下几种:

RAID 0	存取速度最快没有容错
RAID 1	完全容错成本高,硬盘使用率低.
RAID 3	写入性能最好没有多任务功能
RAID 4	具备多任务及容错功能 Parity 磁盘驱动器造成性能瓶颈
RAID 5	具备多任务及容错功能写入时有overhead
RAID 0+1	速度快、完全容错成本高

3、Linux RAID 5实验详解

3.1 准备磁盘

假设我有4块硬盘,(没有条件的朋友可以用虚拟机设置出4块硬盘出来).分别为 /dev/sda /dev/sdb /dev/sdc /dev/sdd 首先做的就是分区了.

[root@localhost /]# fdisk /dev/sda
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel. Changes will remain in memory only,
until you decide to write them. After that, of course, the previous
content won't be recoverable.
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
Command (m for help): n #按n创建新分区
Command action
e extended
p primary partition (1-4) #输入p 选择创建主分区
p
Partition number (1-4): 1 #输入 1 创建第一个主分区
First cylinder (1-130, default 1): #直接回车,选择分区开始柱面这里就从 1 开始
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-102, default 130):
Using default value 130
Command (m for help): w #然后输入w写盘
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.

其它分区照这样做全部分出一个区出来.下面是总分区信息:

1	[root@localhost /]# fdisk -l

Disk /dev/sda: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 1 130 1044193+ 83 Linux
Disk /dev/sdb: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 1 130 1044193+ 83 Linux
Disk /dev/sdc: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdc1 1 130 1044193+ 83 Linux
Disk /dev/sdd: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdd1 1 130 1044193+ 83 Linux

3.2 创建RAID

1	[root@localhost ~]# mdadm --create /dev/md0 --level=5 --raid-devices=3 --spare-devices=1 /dev/sd[a-d]1

#意思是创建RAID设备名为md0, 级别为RAID 5
mdadm: array /dev/md0 started. 使用3个设备建立RAID,空余一个做备用.

OK,初步建立了RAID了,我们看下具体情况吧.

1	[root@localhost ~]# mdadm --detail /dev/md0

/dev/md0:
Version : 00.90.01
Creation Time : Fri Aug 3 13:53:34 2007
Raid Level : raid5
Array Size : 2088192 (2039.25 MiB 2138.31 MB)
Device Size : 1044096 (1019.63 MiB 1069.15 MB)
Raid Devices : 3
Total Devices : 4
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Fri Aug 3 13:54:02 2007
State : clean
Active Devices : 3
Working Devices : 4
Failed Devices : 0
Spare Devices : 1
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
0 8 1 0 active sync /dev/sda1
1 8 17 1 active sync /dev/sdb1
2 8 33 2 active sync /dev/sdc1
3 8 49 -1 spare /dev/sdd1
UUID : e62a8ca6:2033f8a1:f333e527:78b0278a
Events : 0.2

3.3 让RAID开机启动

配置RIAD配置文件吧.默认名字为mdadm.conf,这个文件默认是不存在的,要自己建立.该配置文件存在的主要作用是系统启动的时候能够自动加载软RAID，同时也方便日后管理.

说明下,mdadm.conf文件主要由以下部分组成:DEVICES选项制定组成RAID所有设备, ARRAY选项指定阵列的设备名、RAID级别、阵列中活动设备的数目以及设备的UUID号.

[root@localhost ~]# mdadm --detail --scan > /etc/mdadm.conf
[root@localhost ~]# cat /etc/mdadm.conf
ARRAY /dev/md0 level=raid5 num-devices=3 UUID=e62a8ca6:2033f8a1:f333e527:78b0278a
  devices=/dev/sda1,/dev/sdb1,/dev/sdc1,/dev/sdd1

#默认格式是不正确的,需要做以下方式的修改:

[root@localhost ~]# vi /etc/mdadm.conf
[root@localhost ~]# cat /etc/mdadm.conf

devices /dev/sda1,/dev/sdb1,/dev/sdc1,/dev/sdd1
ARRAY /dev/md0 level=raid5 num-devices=3 UUID=e62a8ca6:2033f8a1:f333e527:78b0278a

3.4 将/dev/md0创建文件系统

[root@localhost ~]# mkfs.ext3 /dev/md0
mke2fs 1.35 (28-Feb-2004)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
261120 inodes, 522048 blocks
26102 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
16320 inodes per group
Superblock backups stored on blocks:
    32768, 98304, 163840, 229376, 294912

Writing inode tables: done
Creating journal (8192 blocks): done
Writing 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.内容

3.5 挂载/dev/md0到系统中去,我们实验是否可用

[root@localhost ~]# cd /
[root@localhost /]# mkdir mdadm
[root@localhost /]# mount /dev/md0 /mdadm/
[root@localhost /]# cd /mdadm/
[root@localhost mdadm]# ls
lost+found
[root@localhost mdadm]# cp /etc/services .
[root@localhost mdadm]# ls
lost+found services

好了,如果其中某个硬盘坏了会怎么样呢?系统会自动停止这块硬盘的工作,然后让后备的那块硬盘顶上去工作.我们可以实验下.

1	[root@localhost mdadm]# mdadm /dev/md0 --fail /dev/sdc1

mdadm: set /dev/sdc1 faulty in /dev/md0
[root@localhost mdadm]# cat /proc/mdstat
Personalities : [raid5]
md0 : active raid5 sdc13 sdd1[2] sdb1[1] sda1[0] # F标签以为此盘为fail.
2088192 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]
unused devices:

如果我要移除一块坏的硬盘或添加一块硬盘呢?

3.6 删除一块硬盘

1	[root@localhost mdadm]# mdadm /dev/md0 --remove /dev/sdc1

mdadm: hot removed /dev/sdc1
[root@localhost mdadm]# cat /proc/mdstat
Personalities : [raid5]
md0 : active raid5 sdd1[2] sdb1[1] sda1[0]
2088192 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]
unused devices:

3.7 增加一块硬盘

1	[root@localhost mdadm]# mdadm /dev/md0 --add /dev/sdc1

mdadm: hot added /dev/sdc1
[root@localhost mdadm]# cat /proc/mdstat
Personalities : [raid5]
md0 : active raid5 sdc1[3] sdd1[2] sdb1[1] sda1[0]
2088192 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]
unused devices: