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Detailed explanation of the implementation of software raid 5

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Jun 25, 2017 am 10:09 AM

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Implementation of software raid 5

RAID 5 is a storage solution that takes into account storage performance, data security and storage cost. RAID 5 can be understood as a compromise between RAID 0 and RAID 1. RAID 5 can provide data security for the system, but the level of protection is lower than Mirror and the disk space utilization is higher than Mirror. RAID 5 has a data reading speed similar to RAID 0, but has an additional parity check information, and the writing speed of data is slightly slower than writing to a single disk. At the same time, because multiple data correspond to one parity information, RAID 5 has a higher disk space utilization than RAID 1, and the storage cost is relatively low. It is a solution that is currently used

1 Partition

Here we use the two partitions /dev/sda8 and /dev/sda9 and the two partitions /dev/sdb and /dev/sdc a hard drive.

Note: Remember to change the partition ID to fd

2 Create raid 5

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

[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.

-C Creation mode

-n #: Use # fast devices to create secondary RAID

-l #: Specify the level of RAID to be created

-a{yes|no}: Automatically create the device file of the target RAID device

-c CHUNK_SIZE: Specify the block size

-x #: Specify the number of spare disks, The one placed at the end defaults to the spare disk

3 Create a file system

[root@centos7 ~]# mkfs.ext4 /dev/md5

##4 Mount

(1) Create the mount directory

[root@centos7 ~]# mkdir /mnt/raid5

(2) Mount

[root@centos7 ~]# mount /dev/md5 /mnt/raid5

5 Generate configuration file

[root@centos7 ~]# cat /etc/mdadm.conf

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

View the status of md

[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]

View raid The details

[root@centos7 ~]# 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

can be seen as composite expected, three active devices, one idle (standby) device

6 Disable and Enable

umount /mnt/raid0

mdadm -S /dev/md0

mdadm -A /dev/md0

(1) Disable raid

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

Check and you can see that it has been stopped successfully

[root@centos7 ~]# mdadm -D /dev/md5

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

(2) Enable raid device

[root@centos7 ~]# mdadm -A /dev/md5

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

Check again and find that it has been started successfully

[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 Simulate /dev/sdc damage

[root@centos7 ~]# mdadm /dev/md5 -f /dev/sdc

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

8 Remove /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

可以看到已经移除成功。

Let’s look at the disk situation again

[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

You can see that /dev/sdc no longer belongs to the md5 array

9Add to raid member

[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

You can see that the addition was successful

10 Increase the number of raid members from 3 to 4

Add device /dev/sdd to the array here

[root@centos7 ~]# mdadm -G /dev/md5 -n 4 -a /dev/sdd

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

Check the file System integrity

[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

Synchronize the file system

[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.

Let’s check the /dev/md5 array again

[root@centos7 ~]# 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

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