软件raid 5

软件raid 5的实现

RAID 5 是一种存储性能、数据安全和存储成本兼顾的存储解决方案。 RAID 5可以理解为是RAID 0和RAID 1的折中方案。RAID 5可以为系统提供数据安全保障，但保障程度要比Mirror低而磁盘空间利用率要比Mirror高。RAID 5具有和RAID 0相近似的数据读取速度，只是多了一个奇偶校验信息，写入数据的速度比对单个磁盘进行写入操作稍慢。同时由于多个数据对应一个奇偶校验信息，RAID 5的磁盘空间利用率要比RAID 1高，存储成本相对较低，是目前运用较多的一种解决方案

1 分区

这里使用/dev/sda8、/dev/sda9两分区和/dev/sdb、/dev/sdc两个硬盘。

注意：记得把分区的ID 改为fd

2创建raid 5

mdadm -C /dev/md5 -a yes -l 5 -n 3 -x 1 /dev/sdd1 /dev/sde1 /dev/sdf /dev/sdb2

[[email protected] ~]# mdadm -C /dev/md5 -a yes -l 5 -n 3 -x 1 /dev/sda8 /dev/sda9 /dev/sdb /dev/sdc

mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md5 started.

-C 创建模式

-n #：使用#个快设备来创建次RAID

-l #：指明要创建的RAID 的级别

-a{yes|no}：自动创建目标RAID设备的设备文件

-c CHUNK_SIZE：指明块大小

-x #： 为指定备用磁盘个数，放在最后的默认为备用磁盘

3 创建文件系统

[[email protected] ~]# mkfs.ext4 /dev/md5

4 挂载

（1）创建挂载目录

[[email protected] ~]# mkdir /mnt/raid5

（2）挂载

[[email protected] ~]# mount /dev/md5 /mnt/raid5

5 生成配置文件

[[email protected] ~]# cat /etc/mdadm.conf

ARRAY /dev/md5 metadata=1.2 spares=1 name=centos7.3.loacl:5 UUID=5ec4115c:ab1e25c8:ff36d8a2:74f6fd8a

查看md的状态

[[email protected] ~]# cat /proc/mdstat

Personalities : [raid0] [raid6] [raid5] [raid4]
md5 : active raid5 sdb[4] sdc[3](S) sda9[1] sda8[0]
2095104 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU]

查看raid的详细信息

[[email protected] ~]# mdadm -D /dev/md5

/dev/md5:
Version : 1.2
Creation Time : Tue Apr 25 14:38:54 2017
Raid Level : raid5
Array Size : 2095104 (2046.00 MiB 2145.39 MB)
Used Dev Size : 1047552 (1023.00 MiB 1072.69 MB)
Raid Devices : 3
Total Devices : 4
Persistence : Superblock is persistent

Update Time : Tue Apr 25 14:50:08 2017
State : clean
Active Devices : 3
Working Devices : 4
Failed Devices : 0
Spare Devices : 1

Layout : left-symmetric
Chunk Size : 512K

Name : centos7.3.loacl:5 (local to host centos7.3.loacl)
UUID : 5ec4115c:ab1e25c8:ff36d8a2:74f6fd8a
Events : 18

Number Major Minor RaidDevice State
0 8 8 0 active sync /dev/sda8
1 8 9 1 active sync /dev/sda9
4 8 16 2 active sync /dev/sdb

3 8 32 - spare /dev/sdc

可以看到复合预期，三个活动设备，一个空闲（备用）设备

6 禁用和启用

umount /mnt/raid0

mdadm -S /dev/md0

mdadm -A /dev/md0

（1）停用raid

[[email protected] ~]# umount /mnt/raid5
[[email protected] ~]# mdadm -S /dev/md5
mdadm: stopped /dev/md5

检查一下，可以看到已经停止成功

[[email protected] ~]# mdadm -D /dev/md5

mdadm: cannot open /dev/md5: No such file or directory

（2）启用raid设备

[[email protected] ~]# mdadm -A /dev/md5

mdadm: /dev/md5 has been started with 3 drives and 1 spare.

再来检查一下，发现已经成功启动

[[email protected] ~]# cat /proc/mdstat

Personalities : [raid0] [raid6] [raid5] [raid4]
md5 : active raid5 sda8[0] sdc[3](S) sdb[4] sda9[1]
2095104 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU]

7 模拟/dev/sdc损坏

[[email protected] ~]# mdadm /dev/md5 -f /dev/sdc

mdadm: set /dev/sdc faulty in /dev/md5

8 移除/dev/sdc

[[email protected] ~]# mdadm /dev/md5 -r /dev/sdc
mdadm: hot removed /dev/sdc from /dev/md5

[[email protected] ~]# mdadm -D /dev/md5

/dev/md5:
[……]
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0
[……]
Number Major Minor RaidDevice State
0 8 8 0 active sync /dev/sda8
1 8 9 1 active sync /dev/sda9
4 8 16 2 active sync /dev/sdb

可以看到已经移除成功。

再来看下磁盘情况

[[email protected] ~]# lsblk

NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
fd0 2:0 1 4K 0 disk
sda 8:0 0 20G 0 disk
[……]
├─sda8 8:8 0 1G 0 part
│ └─md5 9:5 0 2G 0 raid5
└─sda9 8:9 0 1G 0 part
└─md5 9:5 0 2G 0 raid5
sdb 8:16 0 1G 0 disk
└─md5 9:5 0 2G 0 raid5
sdc 8:32 0 1G 0 disk
sr0 11:0 1 7.7G 0 rom

可以看到/dev/sdc已经不属于md5阵列

9添加到raid成员

[[email protected] ~]# mdadm /dev/md5 -a /dev/sdc

mdadm: added /dev/sdc

[[email protected] ~]# mdadm -D /dev/md5

/dev/md5:
[……]
Raid Devices : 3
Total Devices : 4
Active Devices : 3
Working Devices : 4
[……]
Number Major Minor RaidDevice State
0 8 8 0 active sync /dev/sda8
1 8 9 1 active sync /dev/sda9
4 8 16 2 active sync /dev/sdb

3 8 32 - spare /dev/sdc

可以看到添加成功

10 增加raid成员数量从3变为4个

这里添加设备/dev/sdd到阵列

[[email protected] ~]# mdadm -G /dev/md5 -n 4 -a /dev/sdd

mdadm: added /dev/sdd
mdadm: Need to backup 3072K of critical section..

检查文件系统完整性

[[email protected] ~]# e2fsck -f /dev/md5

e2fsck 1.42.9 (28-Dec-2013)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/md5: 11/131072 files (0.0% non-contiguous), 17964/523776 blocks

同步文件系统

[[email protected] ~]# resize2fs /dev/md5

resize2fs 1.42.9 (28-Dec-2013)
Resizing the filesystem on /dev/md5 to 785664 (4k) blocks.
The filesystem on /dev/md5 is now 785664 blocks long.

再来查看/dev/md5阵列情况

[[email protected] ~]# mdadm -D /dev/md5

/dev/md5:
Version : 1.2
Creation Time : Tue Apr 25 14:38:54 2017
Raid Level : raid5
Array Size : 3142656 (3.00 GiB 3.22 GB)
Used Dev Size : 1047552 (1023.00 MiB 1072.69 MB)
Raid Devices : 4
Total Devices : 5
Persistence : Superblock is persistent

Update Time : Tue Apr 25 15:13:32 2017
State : clean
Active Devices : 4
Working Devices : 5

Failed Devices : 0
Spare Devices : 1 

Layout : left-symmetric
Chunk Size : 512K

Name : centos7.3.loacl:5 (local to host centos7.3.loacl)
UUID : 5ec4115c:ab1e25c8:ff36d8a2:74f6fd8a
Events : 47

Number Major Minor RaidDevice State
0 8 8 0 active sync /dev/sda8
1 8 9 1 active sync /dev/sda9
4 8 16 2 active sync /dev/sdb
5 8 48 3 active sync /dev/sdd

3 8 32 - spare /dev/sdc