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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36 Responses

  1. Manoj Katkade says:

    Hi Babin,

    We are facing serious issue with RAID-0, we have created RAID-0 using your article in our Production environment. Now the scenario is our RAID-0 disks / mount point got 100% utilized and we want to extend the same RAID-0 volume.

    I have tried to extend the existing RAID-0 array by adding new disk to server. And uses your article Grow Raid Array in Linux to extend the RAID array, but it got failed and it converted existing RAID-0 to RAID-4 and gone in to inactive state.

    Also one of the existing disk got out of RAID-0 array and giving error “mdadm: /dev/md0 is not an active md array – aborting“.

    I do have error screenshot file. Please let me know on which email ID I should send to you.

    Important : Please help to learn us, how to extend existing RAID-0 array in Linux.

    • Mohammad Waseem says:

      Hi Manoj, I am having the same scenario. I have created a raid 0 setup with 2 disks of 50 GB, now disk has been utilized to 100%. Can you please help which document to follow to add new disks in raid array so that my data will be intact

  2. Amit Bhatt says:

    Is it possible to monitor RAID0 failover events. I set-up RAID 0 on a test environment with 2 disks of 1 GB each. Then i removed one of the disk of the disk on a running system. But still I am able to work properly on my RAID 0 filesystem of 2 GB i.e. I am able to create a new file of 2GB.

    Although I have monitor mode setup via mdadm but i believe thats not gonna work as the man page suggests “Monitor one or more md devices and act on any state changes. This is only meaningful for RAID1, 4, 5, 6, 10 or multipath arrays, as only these have interesting state. RAID0 or Linear never have missing, spare, or failed drives, so there is nothing to monitor.”

    So id there there any other way by which whenever a RAID0 disk fails we can get an alert of corruption message while doing anything on filesystem.

    Thanks in advance…..Waiting for your reply..

    • @Amit,

      Yes, we can setup an email alert as below. This will trigger the email when an error or failure in array md0.

      # mdadm –monitor –daemonise –[email protected] –delay=1800 /dev/md0

      Thanks & Regards,
      Babin Lonston

      • Amit Bhatt says:

        Thanks Bobin. This does not seems to be working. However when i am trying to send a test mail using :

        /sbin/mdadm –monitor –scan –test

        then i am getting an e-mail in my mail box.

        Regards,
        Amit

  3. ali nesary says:

    Thanks for this

  4. Josh Van Kley says:

    Thanks for this. I stumbled through countless write ups and reference material before reaching your article. I was able to spin up my secondary RAID 0 caching array easily while following your guide.

  5. Hello,

    Please correct the spelling of word ” defaults” not “deaults” in the entry of fstab file

    Thanks

  6. June says:

    I was able to follow up to step 6. There wasn’t any /etc/mdadm.conf file so I created one, but I couldn’t save the config.

    Here is the script

    [[email protected] ~]$ sudo mdadm -E -s -v >> /etc/mdadm.conf
    -bash: /etc/mdadm.conf: Permission denied

    Please advice on how I can troubleshoot.
    Thanks a lot :)

  7. Mark Miller says:

    Hello, I am getting an error message at Step 4:
    [[email protected] fs1]# mdadm -C /dev/md0 -l raid0 -n 2 /dev/sd[b-c]1
    mdadm: cannot open /dev/sdb1: Device or resource busy

    How can I fix this?

    Regards, Mark

  8. Mark Miller says:

    [[email protected] fs1]# mdadm -C /dev/md0 -l raid0 -n 2 /dev/sd[b-c]1
    mdadm: cannot open /dev/sdb1: Device or resource busy

    • Please try to stop the RAID set md0
      Then reset the superblock for sdb1
      Remove the partition and recreate it.
      Please go through other RAID topics you will find the solution which i have provided in comments.

  9. Raghu S says:

    [[email protected]@example ~]# more /etc/fstab

    #
    # /etc/fstab
    # Created by anaconda on Sat Sep 20 14:54:34 2014
    #
    # 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=afe2e861-fd68-46bd-a8ef-44da85166195 / ext4 defaults 1 1
    UUID=721422a7-a533-4cff-93fc-bc0249e95f96 /boot ext4 defaults 1 2
    UUID=41677dce-cc0e-4f0c-b924-f76b2bb753a6 swap swap defaults 0 0
    tmpfs /dev/shm tmpfs defaults 0 0
    devpts /dev/pts devpts gid=5,mode=620 0 0
    sysfs /sys sysfs defaults 0 0
    proc /proc proc defaults 0 0
    /dev/md0 /mnt/raid0 ext4 deaults 0 0

    /dev/mapper/vg_tec-lv_tec /mnt/lv_tec ext4 deaults 0 0

  10. Raghu S says:

    Hi Babin Lonston,

    have followed your steps in my Vm , works good, But after i reboot my Vm everything is gone (Including Raid also ) !!!

    Fstab entry also i did .

    [[email protected]@example ~]# more /etc/fstab

    #
    # /etc/fstab
    # Created by anaconda on Sat Sep 20 14:54:34 2014
    #
    # 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=afe2e861-fd68-46bd-a8ef-44da85166195 / ext4 defaults 1 1
    UUID=721422a7-a533-4cff-93fc-bc0249e95f96 /boot ext4 defaults 1 2
    UUID=41677dce-cc0e-4f0c-b924-f76b2bb753a6 swap swap defaults 0 0
    tmpfs /dev/shm tmpfs defaults 0 0
    devpts /dev/pts devpts gid=5,mode=620 0 0
    sysfs /sys sysfs defaults 0 0
    proc /proc proc defaults 0 0
    /dev/md0 /mnt/raid0 ext4 deaults 0 0

    /dev/mapper/vg_tec-lv_tec /mnt/lv_tec ext4 deaults 0 0
    [[email protected]@example ~]# mount -a
    mount: special device /dev/md0 does not exist
    mount: special device /dev/mapper/vg_tec-lv_tec does not exist

    EXPECTING YOUR SUGGESTION !!!!!!!

    Thanks
    Raghu S

    • @Raghu adding fstab entry is not enough, you need to save the raid configuration using below command.

      mdadm -E -s -v >> /etc/mdadm.conf

      Pretty sure you have not done the below steps so only you have lost the RAID after a restart.

      • Pow says:

        I did it but just after i restart the system everything i did just vanished, in the first step of booting the “os” i get this message “Wait for mounting press S for skip mounting….”

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