Step-by-Step Guide to Building a Software RAID 5 on Linux with mdadm

Software RAID 5 Implementation

RAID 5 provides a balance of performance, data safety, and cost by combining striping with parity. This guide shows how to set up a RAID 5 array on CentOS 7 using mdadm.

1. Prepare Partitions

Use two partitions on /dev/sda8 and /dev/sda9 together with the whole disks /dev/sdb and /dev/sdc. Remember to change the partition type ID to fd (Linux RAID autodetect).

2. Create RAID 5

mdadm -C /dev/md5 -a yes -l 5 -n 3 -x 1 /dev/sda8 /dev/sda9 /dev/sdb /dev/sdc

Output:

mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md5 started.

3. Create Filesystem

# mkfs.ext4 /dev/md5

4. Mount the Array

# mkdir /mnt/raid5
# mount /dev/md5 /mnt/raid5

5. Generate mdadm Configuration

# cat /etc/mdadm.conf
ARRAY /dev/md5 metadata=1.2 spares=1 name=centos7.3.local:5 UUID=5ec4115c:ab1e25c8:ff36d8a2:74f6fd8a

6. Check RAID Status

# cat /proc/mdstat

Personalities : [raid0] [raid6] [raid5] [raid4]
md5 : active raid5 sdb[4] sdc[3](S) sda9[1] sda8[0]
2095104 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU]

7. Disable and Enable the Array

# umount /mnt/raid5
# mdadm -S /dev/md5   # stop
# mdadm -A /dev/md5   # start

8. Simulate Disk Failure

# mdadm /dev/md5 -f /dev/sdc

9. Remove a Failed Disk

# mdadm /dev/md5 -r /dev/sdc

10. Re‑add a Disk

# mdadm /dev/md5 -a /dev/sdc

11. Expand the Array (Add a Fourth Device)

# mdadm -G /dev/md5 -n 4 -a /dev/sdd

12. Verify Filesystem Integrity and Resize

# e2fsck -f /dev/md5
# resize2fs /dev/md5

13. Final RAID Information

# mdadm -D /dev/md5

The final array contains four active devices and one spare, with a total size of about 3 GiB.