RAID磁盘阵列
在Linux系统中做RAID，磁盘阵列的设备可以是一块磁盘中的三个以上的分区，也可以是三块以上的磁盘，本文主要参几块磁盘为例，来实现RAID5
实验说明：
在VMware中进行，系统中有一块磁盘sda，新添加6块SCSI磁盘，分别为sdb,sdc ,sdd,sde,sdf,sdg,其中4块作为磁盘阵列的设备，1块作为预备(spare)磁盘，还有1块留作备用。
实验步骤:
第一步：先查看一下系统中磁盘设备：fdisk –l (显示结果略)
第二步：接下来开始创建RAID了，主要会用到mdadm命令，使用此命令需要先安装RHEL6安装光盘中自带的mdadm包，如果没有安装，先进行安装。
[root@localhost ~]# mdadm --create --auto=yes /dev/md0--level=5 --raid-devices=4 --spare-devices=1 /dev/sd[b-f]
参数说明：
--create //表示要创建RAID
--auto=yes /dev/md0 //新建立的软件磁盘阵列设备为md0，md序号可以为0-9
--level=5 //磁盘阵列的等级，这里表示创建的是RAID5
--raid-devices //添加作为磁盘阵列用的磁盘的块数
--spare-device //添加作为预备(spare)磁盘的块数
/dev/sd[b-f] //磁盘阵列所使用的设备，还可写成/dev/sdb /dev/sdc /dev/sdd /dev/sde/dev/sdf
另外这条命令也可以简写：
mdadm –C /dev/md0 –l5 –n4 –x1 /dev/sd[b-f]
第三步：查看RAID是否成功创建及是否正常运行，有两种方法（当磁盘容量越大时，磁盘阵列构建的时间越长，所以可能需要等待很长时间才能看到参下信息）：
执行mdadm –detail /dev/md0 命令查看RAID的详细信息：
[root@localhost ~]# mdadm --detail /dev/md0
/dev/md0:
Version: 1.2
Creation Time: Wed Dec 19 02:58:51 2012
Raid Level: raid5
Array Size: 62909952 (60.00 GiB 64.42 GB)
Used Dev Size: 20969984 (20.00 GiB 21.47 GB)
Raid Devices: 4
Total Devices: 5
Persistence: Superblock is persistent
Update Time: Wed Dec 19 03:10:38 2012
State: clean
Active Devices: 4
Working Devices : 5
Failed Devices: 0
Spare Devices: 1
Layout: left-symmetric
Chunk Size: 512K
Name: localhost.localdomain:0 (local to hostlocalhost.localdomain)
UUID: 0459e403:4ba8e027:08852362:64f3d361
Events: 26
Number Major Minor RaidDevice State
0 8 16 0 active sync /dev/sdb
1 8 32 1 active sync /dev/sdc
2 8 48 2 active sync /dev/sdd
5 8 64 3 active sync /dev/sde
4 8 80 - spare /dev/sdf
查看/proc/mdstat文件，可以比较简单明了的查看RAID创建各运行的情况
[root@localhost ~]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sde[5] sdf[4](S) sdd[2] sdc[1]sdb[0]
62909952blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3] [UUU_]
[>....................] recovery = 3.8% (807680/20969984) finish=12.8minspeed=26054K/sec
unused devices: <none>
注意：黄色部分代表md建立的过程，
S 代表预备（spare）磁盘，UUUU代表正常，出现_表示不正常，
当md建立完成后，就显示正常，（大概3分钟OK）
执行mdadm -Q /dev/md0 //-Q用来查询设备信息
[root@localhost ~]# mdadm -Q /dev/md0
/dev/md0: 59.100GiB raid5 4 devices, 1 spare. Usemdadm --detail for more detail.
第四步：格式化并且挂载使用创建的RAID
[root@localhost ~]# mkfs.ext4 /dev/md0
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=128 blocks, Stripe width=384 blocks
3932160 inodes, 15727488 blocks
786374 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=0
480 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
32768,98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000,7962624, 11239424
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accountinginformation: done
This filesystem will be automatically checked every 23mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
[root@localhost ~]# mkdir /raid5
[root@localhost ~]# mount /dev/md0 /raid5/
查看新挂的RAID是否可以使用
[root@localhost ~]# df -Th
Filesystem Type Size Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root
ext4 19G 5.1G 13G 30% /
tmpfs tmpfs 250M 264K 250M 1% /dev/shm
/dev/sda1 ext4 485M 30M 430M 7% /boot
/dev/sr0 iso9660 2.9G 2.9G 0 100% /media/RHEL_6.1 i386 Disc 1
/dev/md0 ext4 60G 180M 56G 1% /raid5
[root@localhost ~]# cd /raid5/
[root@localhost raid5]# touch a.txt
[root@localhostraid5]# cp /etc/passwd ./
[root@localhost raid5]# ls
a.txt lost+found passwd
第五步：设置开机自动RAID以及自动挂载：
先建立/etc/mdadm.conf这个配置文件
[root@localhost raid5]# mdadm --detail /dev/md0 | grep-i UUID > /etc/mdadm.conf
上面建立的这个文件需要作小小的修改：
[root@localhost raid5]# vi /etc/mdadm.conf
ARRAY /dev/md0 UUID=0459e403:4ba8e027:08852362:64f3d361
然后再修改/etc/fstab文件，设置开机自动挂载：
[root@localhost raid5]# vi /etc/fstab
/dev/md0 /raid5 ext4 defaults 0 0
重启系统，就可以检查开机自动挂载有没有设置成功了！
第六步：模拟RAID5中一块磁盘损坏，检验spare磁盘的功能（raid5中允许一块磁盘损坏，我们所设置的那1块spare磁盘会立即替代损坏的磁盘，进行RAID的重建，保障数据的安全）
[root@localhost raid5]# mdadm --manage /dev/md0 --fail/dev/sdd
mdadm: set /dev/sdd faulty in /dev/md0
//使用此命令设置磁盘sdd成为出错的状态
来查看一下：mdadm –detail /dev/md0
[root@localhost raid5]# mdadm --detail /dev/md0
/dev/md0:
Version: 1.2
Creation Time: Wed Dec 19 02:58:51 2012
Raid Level: raid5
Array Size: 62909952 (60.00 GiB 64.42 GB)
Used Dev Size: 20969984 (20.00 GiB 21.47 GB)
Raid Devices: 4
Total Devices: 5
Persistence: Superblock is persistent
Update Time: Wed Dec 19 03:52:46 2012
State: clean, degraded, recovering
Active Devices: 3
Working Devices : 4
Failed Devices: 1
Spare Devices: 1
Layout: left-symmetric
Chunk Size: 512K
Rebuild Status: 11% complete
Name: localhost.localdomain:0 (local to hostlocalhost.localdomain)
UUID: 0459e403:4ba8e027:08852362:64f3d361
Events: 29
Number Major Minor RaidDevice State
0 8 16 0 active sync /dev/sdb
1 8 32 1 active sync /dev/sdc
4 8 80 2 spare rebuilding /dev/sdf
5 8 64 3 active sync /dev/sde
2 8 48 - faulty spare /dev/sdd
可以查看cat /proc/mdstat文件查看RAID5的重建过程
[root@localhost raid5]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sde[5] sdf[4] sdd[2](F) sdc[1]sdb[0]
62909952blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3] [UU_U]
[=====>...............] recovery = 28.2% (5922304/20969984)finish=8.5min speed=29268K/sec
unused devices: <none>
再来看一下重建后的结果
[root@localhost raid5]# mdadm --detail /dev/md0
/dev/md0:
Version: 1.2
Creation Time: Wed Dec 19 02:58:51 2012
Raid Level: raid5
Array Size: 62909952 (60.00 GiB 64.42 GB)
Used Dev Size: 20969984 (20.00 GiB 21.47 GB)
Raid Devices: 4
Total Devices: 5
Persistence: Superblock is persistent
Update Time: Wed Dec 19 04:04:08 2012
State: clean
Active Devices: 4
Working Devices : 4
Failed Devices: 1
Spare Devices: 0
Layout: left-symmetric
Chunk Size: 512K
Name: localhost.localdomain:0 (local to hostlocalhost.localdomain)
UUID: 0459e403:4ba8e027:08852362:64f3d361
Events: 65
Number Major Minor RaidDevice State
0 8 16 0 active sync /dev/sdb
1 8 32 1 active sync /dev/sdc
4 8 80 2 active sync /dev/sdf
5 8 64 3 active sync /dev/sde
2 8 48 - faulty spare /dev/sdd
[root@localhost raid5]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sde[5] sdf[4] sdd[2](F) sdc[1]sdb[0]
62909952blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU]
unused devices: <none>
/raid5 还可以正常使用
[root@localhost ~]# cd /raid5/
[root@localhost raid5]# ls
a.txt lost+found passwd
[root@localhost raid5]# touch b.txt
[root@localhost raid5]# ls
a.txt b.txt lost+found passwd
第七步：将出错的磁盘删除并加入新的磁盘
先删除损坏的磁盘sdd
[root@localhost raid5]# mdadm --manage /dev/md0--remove /dev/sdd
mdadm: hot removed /dev/sdd from /dev/md0
再添加一块新的磁盘作为spare磁盘
[root@localhost raid5]# mdadm --manage /dev/md0 --add/dev/sdg
mdadm: added /dev/sdg --添加新的磁盘sdd
然后在来查看下，执行一下命令
[root@localhost raid5]# mdadm --detail /dev/md0
/dev/md0:
Version: 1.2
Creation Time: Wed Dec 19 02:58:51 2012
Raid Level: raid5
Array Size: 62909952 (60.00 GiB 64.42 GB)
Used Dev Size: 20969984 (20.00 GiB 21.47 GB)
Raid Devices: 4
Total Devices: 5
Persistence: Superblock is persistent
Update Time: Wed Dec 19 04:12:20 2012
State: clean
Active Devices: 4
Working Devices : 5
Failed Devices: 0
Spare Devices: 1
Layout: left-symmetric
Chunk Size: 512K
Name: localhost.localdomain:0 (local to hostlocalhost.localdomain)
UUID: 0459e403:4ba8e027:08852362:64f3d361
Events: 67
Number Major Minor RaidDevice State
0 8 16 0 active sync /dev/sdb
1 8 32 1 active sync /dev/sdc
4 8 80 2 active sync /dev/sdf
5 8 64 3 active sync /dev/sde
6 8 96 - spare /dev/sdg
第八步：关闭RAID的方法：
当你不再需要你设置的RAID的，可以用以下方法关闭
卸载/dev/md0 并且删除或注释掉/etc/fstab文件中的配置
[root@localhost~]# umount /dev/md0
[root@localhost~]#vi /etc/fstab
#UUID=6d2590e4-20e9-4d54-9a37-1975fb9fcf47/raid5 ext4 defaults 0 0
使用命令mdadm关闭/dev/md0 并注释掉/etc/mdadm.conf中的设置
[root@localhost ~]# vi /etc/mdadm.conf
#ARRAY /dev/md0 UUID=0459e403:4ba8e027:08852362:64f3d361
将md0阵列中活跃磁盘先模拟故障(--fail)在删除磁盘（--remove），最后执行下面的命令关闭raid
[root@localhost raid5]# mdadm --manage /dev/md0 --fail/dev/sdb
mdadm: set /dev/sdb faulty in /dev/md0
[root@localhost raid5]# mdadm --manage /dev/md0 --fail/dev/sdc
mdadm: set /dev/sdc faulty in /dev/md0
[root@localhost raid5]# mdadm --manage /dev/md0 --fail/dev/sdd
mdadm: set /dev/sdd faulty in /dev/md0
[root@localhost raid5]# mdadm --manage /dev/md0 --fail/dev/sde
mdadm: set /dev/sde faulty in /dev/md0
[root@localhost raid5]# mdadm --manage /dev/md0 --fail/dev/sdf
mdadm: set /dev/sdf faulty in /dev/md0
[root@localhost raid5]# mdadm --manage /dev/md0 --fail/dev/sdg
mdadm: set /dev/sdg faulty in /dev/md0
[root@localhost ~]# mdadm --stop /dev/md0
mdadm: stopped /dev/md0
RAID0和RAID1等同于RAID5
RAID0：并行读写数据
RAID1：镜像磁盘阵列
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