Creating an EVS-based RAID Array Using mdadm

Scenarios

This section shows how to create a RAID 10 array using mdadm.

In this example, the ECS runs CentOS 7.5 64bit. Configurations vary depending on the OS running on the ECS. This section is used for reference only. For the detailed operations and differences, see the corresponding OS documents.

Procedure

Check and take note of the device names.

fdisk -l | grep /dev/vd | grep -v vda

Information similar to the following is displayed:

[root@ecs-raid10 ~]# fdisk -l | grep /dev/vd | grep -v vda
Disk /dev/vdb: 10.7 GB, 10737418240 bytes, 20971520 sectors
Disk /dev/vdc: 10.7 GB, 10737418240 bytes, 20971520 sectors
Disk /dev/vdd: 10.7 GB, 10737418240 bytes, 20971520 sectors
Disk /dev/vde: 10.7 GB, 10737418240 bytes, 20971520 sectors

In the command output, four disks are attached to the ECS, and the device names are /dev/vdb, /dev/vdc, /dev/vdd, and /dev/vde, respectively.

Install mdadm.

yum install mdadm -y

mdadm is a utility to create and manage software RAID arrays on Linux. Ensure that an EIP has been bound to the ECS where mdadm is to be installed.
Information similar to the following is displayed:
```
[root@ecs-raid10 ~]# yum install mdadm -y
......
Installed:
  mdadm.x86_64 0:4.0-13.el7

Dependency Installed:
  libreport-filesystem.x86_64 0:2.1.11-40.el7.centos

Complete!
```
Create a RAID array using the four disks queried in 2.

mdadm -Cv <RAID-array-device-name> -a yes -n <disk-quantity> -l <RAID-level> <device-name-of-disk1> <device-name-of-disk2> <device-name-of-disk3> <device-name-of-disk4>
Parameter description:
- <RAID-array-device-name>: The value can be user-definable. In this example, /dev/md0 is used.
- <disk-quantity>: Set this parameter based on the actual condition. In this example, RAID 10 is created, and at least four disks are required.
  The minimum number of disks required varies depending on the RAID level. For details, see Overview of Using EVS Disks to Create RAID Arrays.
- <RAID-level>: Set this parameter based on the actual condition. In this example, set it to RAID 10.
- <device-name-of-the-disk>: Enter the device names of all the disks that will be used to create the RAID array. Multiple names are separated with spaces.
Example command:

mdadm -Cv /dev/md0 -a yes -n 4 -l 10 /dev/vdb /dev/vdc /dev/vdd /dev/vde
Information similar to the following is displayed:
```
[root@ecs-raid10 ~]# mdadm -Cv /dev/md0 -a yes -n 4 -l 10 /dev/vdb /dev/vdc /dev/vdd /dev/vde
mdadm: layout defaults to n2
mdadm: layout defaults to n2
mdadm: chunk size defaults to 512K
mdadm: size set to 10476544K
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
```

Format the created RAID array.

mkfs.<file-system-format> <device-name-of-the-RAID-array>

Example command:

mkfs.ext4 /dev/md0

Information similar to the following is displayed:

[root@ecs-raid10 ~]# mkfs.ext4 /dev/md0
mke2fs 1.42.9 (28-Dec-2013)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=128 blocks, Stripe width=256 blocks
1310720 inodes, 5238272 blocks
261913 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=2153775104
160 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

Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

Create a mount point.

mkdir <mount-point>

Example command:

mkdir /RAID10
Mount the RAID array.

mount <RAID-array-device-name> <mount-point>

Example command:

mount /dev/md0 /RAID10

Check the mount result.

df -h

Information similar to the following is displayed:

[root@ecs-raid10 ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/vda2        39G  1.5G   35G   5% /
devtmpfs        911M     0  911M   0% /dev
tmpfs           920M     0  920M   0% /dev/shm
tmpfs           920M  8.6M  911M   1% /run
tmpfs           920M     0  920M   0% /sys/fs/cgroup
/dev/vda1       976M  146M  764M  17% /boot
tmpfs           184M     0  184M   0% /run/user/0
/dev/md0         20G   45M   19G   1% /RAID10

Perform the following operations to enable auto mount of the RAID array at the system start:

Open the /etc/fstab file.
vi /etc/fstab

Press i to enter editing mode.

Information similar to the following is displayed:

[root@ecs-raid10 ~]# vi /etc/fstab

#
# /etc/fstab
# Created by anaconda on Tue Nov  7 14:28:26 2017
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=27f9be47-838b-4155-b20b-e4c5e013cdf3 /                       ext4    defaults        1 1
UUID=2b2000b1-f926-4b6b-ade8-695ee244a901 /boot                   ext4    defaults        1 2

Add the following information to the end of the file:

/dev/md0                                  /RAID10                 ext4    defaults        0 0

Press Esc, enter :wq!, and press Enter.
The system saves the modifications and exits the vi editor.

View the RAID array information.

mdadm -D <RAID-array-device-name>

Example command:

mdadm -D /dev/md0

Information similar to the following is displayed:

[root@ecs-raid10 ~]# mdadm -D /dev/md0
/dev/md0:
           Version : 1.2
     Creation Time : Thu Nov  8 15:49:02 2018
        Raid Level : raid10
        Array Size : 20953088 (19.98 GiB 21.46 GB)
     Used Dev Size : 10476544 (9.99 GiB 10.73 GB)
      Raid Devices : 4
     Total Devices : 4
       Persistence : Superblock is persistent

       Update Time : Thu Nov  8 16:15:11 2018
             State : clean
    Active Devices : 4
   Working Devices : 4
    Failed Devices : 0
     Spare Devices : 0

            Layout : near=2
        Chunk Size : 512K

Consistency Policy : resync

              Name : ecs-raid10.novalocal:0  (local to host ecs-raid10.novalocal)
              UUID : f400dbf9:60d211d9:e006e07b:98f8758c
            Events : 19

    Number   Major   Minor   RaidDevice State
       0     253       16        0      active sync set-A   /dev/vdb
       1     253       32        1      active sync set-B   /dev/vdc
       2     253       48        2      active sync set-A   /dev/vdd
       3     253       64        3      active sync set-B   /dev/vde

Parent topic: Implementation Procedure

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