軟件raid 5的實(shí)現(xiàn)

RAID 5 是一種存儲(chǔ)性能、數(shù)據(jù)安全和存儲(chǔ)成本兼顧的存儲(chǔ)解決方案。RAID 5可以理解為是RAID 0和RAID 1的折中方案。RAID 5可以為系統(tǒng)提供數(shù)據(jù)安全保障，但保障程度要比Mirror低而磁盤(pán)空間利用率要比Mirror高。RAID 5具有和RAID 0相近似的數(shù)據(jù)讀取速度，只是多了一個(gè)奇偶校驗(yàn)信息，寫(xiě)入數(shù)據(jù)的速度比對(duì)單個(gè)磁盤(pán)進(jìn)行寫(xiě)入操作稍慢。同時(shí)由于多個(gè)數(shù)據(jù)對(duì)應(yīng)一個(gè)奇偶校驗(yàn)信息，RAID 5的磁盤(pán)空間利用率要比RAID 1高，存儲(chǔ)成本相對(duì)較低，是目前運(yùn)用較多的一種解決方案。

1 分區(qū)

這里使用/dev/sda8、/dev/sda9兩分區(qū)和/dev/sdb、/dev/sdc兩個(gè)硬盤(pán)。

注意：記得把分區(qū)的ID 改為fd

2創(chuàng)建raid 5

[root@centos7 ~]# 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.

- #：指明要?jiǎng)?chuàng)建的RAID 的級(jí)別

-a{yes|no}：自動(dòng)創(chuàng)建目標(biāo)RAID設(shè)備的設(shè)備文件

-c CHUNK_SIZE：指明塊大小

-x #：為指定備用磁盤(pán)個(gè)數(shù)，放在最后的默認(rèn)為備用磁盤(pán)

3 創(chuàng)建文件系統(tǒng)

4 掛載

（1）創(chuàng)建掛載目錄

（2）掛載

5 生成配置文件

[root@centos7 ~]# cat /etc/mdadm.conf
 
ARRAY /dev/md5 metadata=1.2 spares=1 name=centos7.3.loacl:5 UUID=5ec4115cff36d8a2:74f6fd8a

查看md的狀態(tài)

[root@centos7 ~]# 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的詳細(xì)信息

[root@centos7 ~]# mdadm -D /dev/md5
 
/dev/md5:
Version : 1.2
Creation Time : Tue Apr 25 1454 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 1408 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 : 5ec4115cff36d8a2:74f6fd8a
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

可以看到復(fù)合預(yù)期，三個(gè)活動(dòng)設(shè)備，一個(gè)空閑（備用）設(shè)備

6 禁用和啟用

umount /mnt/raid0
 
mdadm -S /dev/md0
 
mdadm -A /dev/md0

（1）停用raid

[root@centos7 ~]# umount /mnt/raid5
[root@centos7 ~]# mdadm -S /dev/md5
mdadm: stopped /dev/md5

檢查一下，可以看到已經(jīng)停止成功

[root@centos7 ~]# mdadm -D /dev/md5
 
mdadm: cannot open /dev/md5: No such file or directory

（2）啟用raid設(shè)備

[root@centos7 ~]# mdadm -A /dev/md5
 
mdadm: /dev/md5 has been started with 3 drives and 1 spare.

再來(lái)檢查一下，發(fā)現(xiàn)已經(jīng)成功啟動(dòng)

[root@centos7 ~]# 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 模擬/dev/sdc損壞

[root@centos7 ~]# mdadm /dev/md5 -f /dev/sdc
 
mdadm: set /dev/sdc faulty in /dev/md5

8 移除/dev/sdc

[root@centos7 ~]# mdadm /dev/md5 -r /dev/sdc
mdadm: hot removed /dev/sdc from /dev/md5
 
[root@centos7 ~]# 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

可以看到已經(jīng)移除成功。

再來(lái)看下磁盤(pán)情況

[root@centos7 ~]# 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已經(jīng)不屬于md5陣列

9添加到raid成員

[root@centos7 ~]# mdadm /dev/md5 -a /dev/sdc
 
mdadm:added/dev/sdc
[root@centos7 ~]# 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成員數(shù)量從3變?yōu)?個(gè)

這里添加設(shè)備/dev/sdd到陣列

[root@centos7 ~]# mdadm -G /dev/md5 -n 4 -a /dev/sdd
 
mdadm: added /dev/sdd
mdadm: Need to backup 3072K of critical section..

檢查文件系統(tǒng)完整性

[root@centos7 ~]# 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

同步文件系統(tǒng)

[root@centos7 ~]# 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.

再來(lái)查看/dev/md5陣列情況

[root@centos7 ~]# mdadm -D /dev/md5
 
/dev/md5:
Version : 1.2
Creation Time : Tue Apr 25 1454 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 1532 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 : 5ec4115cff36d8a2:74f6fd8a
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