Taken and simplified from here.
RAID 10 is a combination of RAID 0 and RAID 1 to form a RAID 10. To setup Raid 10, we need at least 4 disks.
Here we will use both RAID 0 and RAID 1 to perform a Raid 10 setup with minimum of 4 drives. Assume, that we’ve some data saved to logical volume, which is created with RAID 10. Just for an example, if we are saving a data “apple” this will be saved under all 4 disk by this following method.
Creating RAID 10
Using RAID 0 it will save as “A” in first disk and “p” in the second disk, then again “p” in first disk and “l” in second disk. Then “e” in first disk, like this it will continue the Round robin process to save the data. From this we come to know that RAID 0 will write the half of the data to first disk and other half of the data to second disk.
In RAID 1 method, same data will be written to other 2 disks as follows. “A” will write to both first and second disks, “P” will write to both disk, Again other “P” will write to both the disks. Thus using RAID 1 it will write to both the disks. This will continue in round robin process.
Now you all came to know that how RAID 10 works by combining of both RAID 0 and RAID 1. If we have 4 number of 20 GB size disks, it will be 80 GB in total, but we will get only 40 GB of Storage capacity, the half of total capacity will be lost for building RAID 10.
Requirements
In RAID 10, we need minimum of 4 disks, the first 2 disks for RAID 0 and other 2 Disks for RAID 1. Like I said before, RAID 10 is just a Combine of RAID 0 & 1. If we need to extended the RAID group, we must increase the disk by minimum 4 disks.
My Server Setup
Operating System : CentOS 6.5 Final
IP Address : 192.168.0.229
Hostname : rd10.tecmintlocal.com
Disk 1 [20GB] : /dev/sdd
Disk 2 [20GB] : /dev/sdc
Disk 3 [20GB] : /dev/sdd
Disk 4 [20GB] : /dev/sde
There are two ways to setup RAID 10, but here I’m going to show you both methods, but I prefer you to follow the first method, which makes the work lot easier for setting up a RAID 10.
Method 1: Setting Up Raid 10
-
First, verify that all the 4 added disks are detected or not using the following command.
ls -l /dev | grep sd -
Once the four disks are detected, it’s time to check for the drives whether there is already any raid existed before creating a new one.
mdadm -E /dev/sd[b-e] mdadm --examine /dev/sdb /dev/sdc /dev/sdd /dev/sde
Verify 4 Added Disks
Note: In the above output, you see there isn’t any super-block detected yet, that means there is no RAID defined in all 4 drives.
Step 1: Drive Partitioning for RAID
-
Now create a new partition on all 4 disks (/dev/sdb, /dev/sdc, /dev/sdd and /dev/sde) using the ‘fdisk’ tool.
fdisk /dev/sdb fdisk /dev/sdc fdisk /dev/sdd fdisk /dev/sde
Create /dev/sdb Partition
Let me show you how to partition one of the disk (/dev/sdb) using fdisk, this steps will be the same for all the other disks too.
fdisk /dev/sdb
Please use the below steps for creating a new partition on /dev/sdb drive.
- Press ‘n‘ for creating new partition.
- Then choose ‘P‘ for Primary partition.
- Then choose ‘1‘ to be the first partition.
- Next press ‘p‘ to print the created partition.
- Change the Type, If we need to know the every available types Press ‘L‘.
- Here, we are selecting ‘fd‘ as my type is RAID.
- Next press ‘p‘ to print the defined partition.
- Then again use ‘p‘ to print the changes what we have made.
- Use ‘w‘ to write the changes.
Disk sdb Partition
Note: Please use the above same instructions for creating partitions on other disks (sdc, sdd sdd sde).
4. After creating all 4 partitions, again you need to examine the drives for any already existing raid using the following command.
mdadm -E /dev/sd[b-e]
mdadm -E /dev/sd[b-e]1
OR
mdadm --examine /dev/sdb /dev/sdc /dev/sdd /dev/sde
mdadm --examine /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1
Check All Disks for Raid
Note: The above outputs shows that there isn’t any super-block detected on all four newly created partitions, that means we can move forward to create RAID 10 on these drives.
Step 2: Creating ‘md’ RAID Device
-
Now it’s time to create a ‘md’ (i.e. /dev/md0) device, using ‘mdadm’ raid management tool. Before, creating device, your system must have ‘mdadm’ tool installed, if not install it first.
yum install mdadm
Once ‘mdadm’ tool installed, you can now create a ‘md’ raid device using the following command.
mdadm --create /dev/md0 --level=10 --raid-devices=4 /dev/sd[b-e]1
-
Next verify the newly created raid device using the ‘cat’ command.
cat /proc/mdstat
Loading the modules
echo "modprobe raid10" > /etc/sysconfig/modules/raid.modules
modprobe raid10
chmod a+x /etc/sysconfig/modules/raid.modules
Create md raid Device
-
Next, examine all the 4 drives using the below command. The output of the below command will be long as it displays the information of all 4 disks.
mdadm --examine /dev/sd[b-e]1 -
Next, check the details of Raid Array with the help of following command.
mdadm --detail /dev/md0
Check Raid Array Details
Note: You see in the above results, that the status of Raid was active and re-syncing.
Step 3: Creating Filesystem
-
Create a file system using ext4 for ‘md0’ and mount it under ‘/mnt/raid10‘. Here, I’ve used ext4, but you can use any filesystem type if you want.
mkfs.ext4 /dev/md0
Create md Filesystem
10. After creating filesystem, mount the created file-system under ‘/mnt/raid10‘ and list the contents of the mount point using ‘ls -l’ command.
mkdir /mnt/raid10
mount /dev/md0 /mnt/raid10/
ls -l /mnt/raid10/
Next, add some files under mount point and append some text in any one of the file and check the content.
touch /mnt/raid10/raid10_files.txt
ls -l /mnt/raid10/
echo "raid 10 setup with 4 disks" > /mnt/raid10/raid10_files.txt
cat /mnt/raid10/raid10_files.txt
Mount md Device
11. For automounting, open the ‘/etc/fstab‘ file and append the below entry in fstab, may be mount point will differ according to your environment.
vim /etc/fstab
/dev/md0 /mnt/raid10 ext4 defaults 0 0
To save and quit type.
wq!.
AutoMount md Device
12. Next, verify the ‘/etc/fstab‘ file for any errors before restarting the system using ‘mount -a‘ command.
mount -av
Check Errors in Fstab
Step 4: Save RAID Configuration
-
By default RAID don’t have a config file, so we need to save it manually after making all the above steps, to preserve these settings during system boot.
mdadm --detail --scan --verbose >> /etc/mdadm.conf
Save Raid10 Configuration
That’s it, we have created RAID 10 using this method.
And it still gets you arrested, so not worth the risk.