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软RAID 5建立过程

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
  RAID可分为以下几种,做个表格认识下:
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
 
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.
[[email protected] /]# 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:
[[email protected] /]# 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

 
下一步就是创建RAID了.
[[email protected] ~]# 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.
[[email protected] ~]# 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
 
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.
[[email protected] ~]# mdadm –detail –scan > /etc/mdadm.conf
[[email protected] ~]# 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:
[[email protected] ~]# vi /etc/mdadm.conf
[[email protected] ~]# 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
 
将/dev/md0创建文件系统,
[[email protected] ~]# 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
 
挂载/dev/md0到系统中去,我们实验是否可用:
[[email protected] ~]# cd /
[[email protected] /]# mkdir mdadm
[[email protected] /]# mount /dev/md0 /mdadm/
[[email protected] /]# cd /mdadm/
[[email protected] mdadm]# ls
lost+found
[[email protected] mdadm]# cp /etc/services .
[[email protected] 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.
[[email protected] mdadm]# mdadm /dev/md0 –fail /dev/sdc1
mdadm: set /dev/sdc1 faulty in /dev/md0
[[email protected] mdadm]# cat /proc/mdstat
Personalities : [raid5]
md0 : active raid5 sdc1[3](F) 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: <none>
 
如果我要移除一块坏的硬盘或添加一块硬盘呢?
#删除一块硬盘
[[email protected] mdadm]# mdadm /dev/md0 –remove /dev/sdc1
mdadm: hot removed /dev/sdc1
[[email protected] 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: <none>
#增加一块硬盘
[[email protected] mdadm]# mdadm /dev/md0 –add /dev/sdc1
mdadm: hot added /dev/sdc1
[[email protected] 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: <none>
 
over commit!