What Is RAID ?
Table of Contents
In this article we are going to discuss how to create raid in linux.
RAID is a method of using multiple hard drives to act as one and purposes of data redundancy, performance improvement, or both.
Purposes of RAID (Redundant Array of Inexpensive Disks):
Expand drive capacity: RAID 0. If you have 2 x 500 GB HDD then total space become 1 TB.
Prevent data loss in case of drive failure: For example RAID 1, RAID 5, RAID 6, and RAID 1+0 or 0+1.
We are going to creating a software RAID
Step 1: Creating a Partition
Creating a physical volume:
#fdisk -c /dev/sdb
press “p” (for print)
press “n” for new partition
press “p” for primary partition “e” for extended partition
press “t” for partition ID
give “fd” for RAID partition
press “w” for save and quit
Sample Output:
[root@localhost ~]# fdisk -l | grep -i “/dev/sd”
Disk /dev/sda: 21.5 GB, 21474836480 bytes, 41943040 sectors
/dev/sda1 * 2048 616447 307200 83 Linux
/dev/sda2 616448 4810751 2097152 82 Linux swap / Solaris
/dev/sda3 4810752 41943039 18566144 83 Linux
Disk /dev/sdb: 1073 MB, 1073741824 bytes, 2097152 sectors
Disk /dev/sdc: 1073 MB, 1073741824 bytes, 2097152 sectors
Disk /dev/sdd: 1073 MB, 1073741824 bytes, 2097152 sectors
Disk /dev/sde: 1073 MB, 1073741824 bytes, 2097152 sectors
[root@localhost ~]# fdisk -c /dev/sdb
Welcome to fdisk (util-linux 2.23.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help): n
Partition type:
p primary (0 primary, 0 extended, 4 free)
e extended
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-2097151, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-2097151, default 2097151):
Using default value 2097151
Partition 1 of type Linux and of size 1023 MiB is set
Command (m for help): t
Selected partition 1
Hex code (type L to list all codes): fd
Changed type of partition ‘Linux’ to ‘Linux raid autodetect’
Command (m for help): p
Disk /dev/sdb: 1073 MB, 1073741824 bytes, 2097152 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x0449f63b
Device Boot Start End Blocks Id System
/dev/sdb1 2048 2097151 1047552 fd Linux raid autodetect
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
Note: We can create a RAID without partitioning of the disk. For RAID 0, need 2 disks.
Step 2: Create A RAID
#mdadm –create /dev/md0 –level=0 –raid-devices=2 /dev/sdb1 /dev/sdc1
Sample Output:
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
Step 3: Verify The RAID
#mdadm –detail /dev/md0
Sample Output:
[root@localhost ~]# mdadm –detail /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Fri Sep 17 13:30:58 2021
Raid Level : raid0
Array Size : 2091008 (2042.00 MiB 2141.19 MB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Fri Sep 17 13:30:58 2021
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Chunk Size : 512K
Consistency Policy : none
Name : localhost.localdomain:0 (local to host localhost.localdomain)
UUID : 243650f8:d2c38bdc:b0ef513e:0edd6d6b
Events : 0
Number Major Minor RaidDevice State
0 8 17 0 active sync /dev/sdb1
1 8 33 1 active sync /dev/sdc1
