Creating Software RAID0 (Stripe) on ‘Two Devices’ Using ‘mdadm’ Tool in Linux – Part 2

RAID is Redundant Array of Inexpensive disks, used for high availability and reliability in large scale environments, where data need to be protected than normal use. Raid is just a collection of disks in a pool to become a logical volume and contains an array. A combine drivers makes an array or called as set of (group).

RAID can be created, if there are minimum 2 number of disk connected to a raid controller and make a logical volume or more drives can be added in an array according to defined RAID Levels. Software Raid are available without using Physical hardware those are called as software raid. Software Raid will be named as Poor man raid.

Setup RAID0 in Linux

Setup RAID0 in Linux

Main concept of using RAID is to save data from Single point of failure, means if we using a single disk to store the data and if it’s failed, then there is no chance of getting our data back, to stop the data loss we need a fault tolerance method. So, that we can use some collection of disk to form a RAID set.

What is Stripe in RAID 0?

Stripe is striping data across multiple disk at the same time by dividing the contents. Assume we have two disks and if we save content to logical volume it will be saved under both two physical disks by dividing the content. For better performance RAID 0 will be used, but we can’t get the data if one of the drive fails. So, it isn’t a good practice to use RAID 0. The only solution is to install operating system with RAID0 applied logical volumes to safe your important files.

  1. RAID 0 has High Performance.
  2. Zero Capacity Loss in RAID 0. No Space will be wasted.
  3. Zero Fault Tolerance ( Can’t get back the data if any one of disk fails).
  4. Write and Reading will be Excellent.

Requirements

Minimum number of disks are allowed to create RAID 0 is 2, but you can add more disk but the order should be twice as 2, 4, 6, 8. If you have a Physical RAID card with enough ports, you can add more disks.

Here we are not using a Hardware raid, this setup depends only on Software RAID. If we have a physical hardware raid card we can access it from it’s utility UI. Some motherboard by default in-build with RAID feature, there UI can be accessed using Ctrl+I keys.

If you’re new to RAID setups, please read our earlier article, where we’ve covered some basic introduction of about RAID.

  1. Introduction to RAID and RAID Concepts
My Server Setup
Operating System :	CentOS 6.5 Final
IP Address	 :	192.168.0.225
Two Disks	 :	20 GB each

This article is Part 2 of a 9-tutorial RAID series, here in this part, we are going to see how we can create and setup Software RAID0 or striping in Linux systems or servers using two 20GB disks named sdb and sdc.

Step 1: Updating System and Installing mdadm for Managing RAID

1. Before setting up RAID0 in Linux, let’s do a system update and then install ‘mdadm‘ package. The mdadm is a small program, which will allow us to configure and manage RAID devices in Linux.

# yum clean all && yum update
# yum install mdadm -y
install mdadm in linux

Install mdadm Tool

Step 2: Verify Attached Two 20GB Drives

2. Before creating RAID 0, make sure to verify that the attached two hard drives are detected or not, using the following command.

# ls -l /dev | grep sd
Check Hard Drives in Linux

Check Hard Drives

3. Once the new hard drives detected, it’s time to check whether the attached drives are already using any existing raid with the help of following ‘mdadm’ command.

# mdadm --examine /dev/sd[b-c]
Check RAID Devices in Linux

Check RAID Devices

In the above output, we come to know that none of the RAID have been applied to these two sdb and sdc drives.

Step 3: Creating Partitions for RAID

4. Now create sdb and sdc partitions for raid, with the help of following fdisk command. Here, I will show how to create partition on sdb drive.

# fdisk /dev/sdb

Follow below instructions for creating partitions.

  1. Press ‘n‘ for creating new partition.
  2. Then choose ‘P‘ for Primary partition.
  3. Next select the partition number as 1.
  4. Give the default value by just pressing two times Enter key.
  5. Next press ‘P‘ to print the defined partition.
Create Partitions in Linux

Create Partitions

Follow below instructions for creating Linux raid auto on partitions.

  1. Press ‘L‘ to list all available types.
  2. Type ‘t‘to choose the partitions.
  3. Choose ‘fd‘ for Linux raid auto and press Enter to apply.
  4. Then again use ‘P‘ to print the changes what we have made.
  5. Use ‘w‘ to write the changes.
Create RAID Partitions

Create RAID Partitions in Linux

Note: Please follow same above instructions to create partition on sdc drive now.

5. After creating partitions, verify both the drivers are correctly defined for RAID using following command.

# mdadm --examine /dev/sd[b-c]
# mdadm --examine /dev/sd[b-c]1
Verify RAID Partitions

Verify RAID Partitions

Step 4: Creating RAID md Devices

6. Now create md device (i.e. /dev/md0) and apply raid level using below command.

# mdadm -C /dev/md0 -l raid0 -n 2 /dev/sd[b-c]1
# mdadm --create /dev/md0 --level=stripe --raid-devices=2 /dev/sd[b-c]1
  1. -C – create
  2. -l – level
  3. -n – No of raid-devices

7. Once md device has been created, now verify the status of RAID Level, Devices and Array used, with the help of following series of commands as shown.

# cat /proc/mdstat
Verify RAID Level

Verify RAID Level

# mdadm -E /dev/sd[b-c]1
Verify RAID Device

Verify RAID Device

# mdadm --detail /dev/md0
Verify RAID Array

Verify RAID Array

Step 5: Assiging RAID Devices to Filesystem

8. Create a ext4 filesystem for a RAID device /dev/md0 and mount it under /dev/raid0.

# mkfs.ext4 /dev/md0
Create ext4 Filesystem in Linux

Create ext4 Filesystem

9. Once ext4 filesystem has been created for Raid device, now create a mount point directory (i.e. /mnt/raid0) and mount the device /dev/md0 under it.

# mkdir /mnt/raid0
# mount /dev/md0 /mnt/raid0/

10. Next, verify that the device /dev/md0 is mounted under /mnt/raid0 directory using df command.

# df -h

11. Next, create a file called ‘tecmint.txt‘ under the mount point /mnt/raid0, add some content to the created file and view the content of a file and directory.

# touch /mnt/raid0/tecmint.txt
# echo "Hi everyone how you doing ?" > /mnt/raid0/tecmint.txt
# cat /mnt/raid0/tecmint.txt
# ls -l /mnt/raid0/
Verify Mount Device

Verify Mount Device

12. Once you’ve verified mount points, it’s time to create an fstab entry in /etc/fstab file.

# vim /etc/fstab

Add the following entry as described. May vary according to your mount location and filesystem you using.

/dev/md0                /mnt/raid0              ext4    defaults         0 0
Add Device to Fstab

Add Device to Fstab

13. Run mount ‘-a‘ to check if there is any error in fstab entry.

# mount -av
Check Errors in Fstab

Check Errors in Fstab

Step 6: Saving RAID Configurations

14. Finally, save the raid configuration to one of the file to keep the configurations for future use. Again we use ‘mdadm’ command with ‘-s‘ (scan) and ‘-v‘ (verbose) options as shown.

# mdadm -E -s -v >> /etc/mdadm.conf
# mdadm --detail --scan --verbose >> /etc/mdadm.conf
# cat /etc/mdadm.conf
Save RAID Configurations

Save RAID Configurations

That’s it, we have seen here, how to configure RAID0 striping with raid levels by using two hard disks. In next article, we will see how to setup RAID5.

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Babin Lonston

I'm Working as a System Administrator for last 10 year's with 4 years experience with Linux Distributions, fall in love with text based operating systems.

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37 Responses

  1. Mark Miller says:

    Hello, I’m stuck at Step 4 with the following error: “cannot open /dev/sdb1: Device or resource busy”

    Any thoughts on how to continue?

    Regards, Mark

    • @Mark Miller

      What does cat /proc/mdstat gives ?

      Assume you have already tried creating raid in this disk before.

      Alright first you need to make the disk super block size to zero.

      Stop the RAID using

      # mdadm –stop /dev/md0

      Then reset the super-block size using below command

      # sudo mdadm –zero-superblock /dev/sda1

      Then remove the partition and recreate and follow the raid creation steps it will work.

    • @Mark Miller

      Assume you have already tried raid setup in this disk.
      Check using # cat /proc/mdstat

      Then stop the RAID using

      # mdadm –manage /dev/md0 –stop

      Then reset the superblock for sda disk

      # mdadm –zero-superblock /dev/sda

      Remove the partitions using fdisk

      Then try to create your RAID let me know how it went through..

  2. Babin says:

    @Priya Dividing and Writing data’s across multiple disk was defined by default Programming no idea were it was defined. RAID 0 was defined as striping. May be kernel Order’s to do RAID 0 to do the striping.

  3. Priya Prabhakar says:

    HI Babin,

    I want to clarify one doubt. When you said that while striping on 2 disk – disk0 and disk1 for RAID-0 The data “TECDH”in which T will be saved in disk0 and E will be saved in disk1 how it knows it should be saved alternatively, somewhere any program or any code that instruct this RAID setup to save the data in this way?

    Thanks in advance.

  4. KM says:

    Great work bro..appreciate it..

  5. k.nitesh says:

    excellent work………..

  6. @Khoi D. Dinh Most welcome, thanks for your feedback

  7. @ Omipenuin

    I’am pretty sure you have not saved the RAID configuration, So what after a restart you can’t see the disks.

    After creating a RAID set first you have to save the RAID configuration by using below command.

    # mdadm –detail –scan –verbose >> /etc/mdadm.conf

    After that just Restart and check for the raid device under

    # ls -l /dev/md0

    It want to list the md0 while we list. Now on-wards follow the below steps. After this Don’t create the file-system in md0 and don’t plan to mount it, cos you need LVM right.

    Then start to create the LVM by creating a Pv

    # pvcreate /dev/md0

    Then create a VG

    # vgcreate vg_tec /dev/md0

    Then create the LV for 500MB (just i’am using for demonstration, use your required size here)

    # lvcreate -n lv_tec -L 500M vg_tec

    Just list the lv using devices if so we can see which device holds the LVM

    # lvs -o+devices

    Then Make the file-system

    # mkfs.ext4 /dev/vg_tec/lv_tec

    Mount the file-system now

    # mkdir -p /mnt/lv_tec

    # mount /dev/vg_tec/lv_tec /mnt/lv_tec/

    # mount -av

    Then add the fstab entry

    # vim /etc/fstab

    Then restart the system

    # init 6

    After restart just check the mount point now

    # df -h

    or check the devices

    # lvs -o+devices

    Still you can’t find the LVM let me know.

    • Omipenuin says:

      Thanks Babin I will do it soon.Will update you about success or failure.

      And again thanks for teaching us in-depth about Software RAID you really spent so much time on this and we are thankful for that.

      • Omipenuin says:

        @Babin. I started to implement all the tuts you taught. Today I worked on this Part2 Implementing RAID0. After creating RAID0 and saving the conf of RAID i implemented LVM on RAID0 .

        And damn it worked. Issue before was just like you said previously i never saved the raid settings previously but now i saved the settings and after restarted system both raid and lvm are available.

        Simply great tutorial. THANKS

  8. Khoi D. Dinh says:

    Thank you.

  9. Omipenuin says:

    Babin when you make a tut for RAID 1 also make LVM on it.

    I tried many times to make LVM work on Software Raid 1 initially it works but when I restart then boom no lvm. LVM gone like never happened

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