詳解Linux環境軟RAID 5建立過程

　　1:Raid定義 　　RAID,全稱Redundant Array of Inexpensive Disks,中文名為廉價磁盤冗余陣列.RAID可分為軟RAID和硬RAID,軟RAID是通過軟件實現多塊硬盤冗余的.而硬RAID是一般通過RAID卡來實現RAID的.前者配置簡單,管理也比較靈活.對於中小企業來說不失為一最佳選擇.硬RAID往往花費比較貴.不過,在性能方面具有一定優勢.   　　2:RAID分類 　　RAID可分為以下幾種,做個表格認識下: RAID 0 存取速度最快 沒有容錯 RAID 1 完全容錯 成本高,硬盤使用率低. RAID 3 寫入性能最好 沒有多任務功能 RAID 4 具備多任務及容錯功能 Parity 磁盤驅動器造成性能瓶頸 RAID 5 具備多任務及容錯功能 寫入時有overhead RAID 0+1 速度快、完全容錯 成本高   　　3:Linux RAID 5實驗詳解   　　假設我有4塊硬盤,(沒有條件的朋友可以用虛擬機設置出4塊硬盤出來).分別為/dev/sda  /dev/sdb  /dev/sdc  /dev/sdd.首先做的就是分區了. [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創建新分區
Command action
e extended
p primary partition (1-4) #輸入p 選擇創建主分區
p
Partition number (1-4): 1 #輸入 1 創建第一個主分區
First cylinder (1-130, default 1): #直接回車,選擇分區開始柱面這裡就從 1 開始
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 #然後輸入w寫盤
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.   　　其它分區照這樣做全部分出一個區出來.下面是總分區信息: [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
  　　下一步就是創建RAID了. [root@localhost ~]# mdadm --create /dev/md0 --level=5 --raid-devices=3 --spare-devices=1 /dev/sd[a-d]1               #意思是創建RAID設備名為md0, 級別為RAID 5
mdadm: array /dev/md0 started.    使用3個設備建立RAID,空余一個做備用.  　　OK,初步建立了RAID了,我們看下具體情況吧. [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   　　讓RAID開機啟動.配置RIAD配置文件吧.默認名字為mdadm.conf,這個文件默認是不存在的,要自己建立.該配置文件存在的主要作用是系統啟動的時候能夠自動加載軟RAID，同時也方便日後管理. 說明下,mdadm.conf文件主要由以下部分組成:DEVICES選項制定組成RAID所有設備, ARRAY選項指定陣列的設備名、RAID級別、陣列中活動設備的數目以及設備的UUID號. [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 #默認格式是不正確的,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
  　　將/dev/md0創建文件系統, [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.內容   　　掛載/dev/md0到系統中去,我們實驗是否可用: [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,如果其中某個硬盤壞了會怎麼樣呢?系統會自動停止這塊硬盤的工作,然後讓後備的那塊硬盤頂上去工作.我們可以實驗下. [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 sdc1[3](F) sdd1[2] sdb1[1] sda1[0] # F標簽以為此盤為fail.
      2088192 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU] unused devices: <none>   　　如果我要移除一塊壞的硬盤或添加一塊硬盤呢? #刪除一塊硬盤 [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: <none> #增加一塊硬盤 [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: <none>   　　好了,結束了,Boss巡邏過來了.