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

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

Output:

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

3. Create Filesystem

<code># mkfs.ext4 /dev/md5</code>

4. Mount the Array

<code># mkdir /mnt/raid5
# mount /dev/md5 /mnt/raid5</code>

5. Generate mdadm Configuration

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

6. Check RAID Status

<code># cat /proc/mdstat</code>

<code>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]</code>

7. Disable and Enable the Array

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

8. Simulate Disk Failure

<code># mdadm /dev/md5 -f /dev/sdc</code>

9. Remove a Failed Disk

<code># mdadm /dev/md5 -r /dev/sdc</code>

10. Re‑add a Disk

<code># mdadm /dev/md5 -a /dev/sdc</code>

11. Expand the Array (Add a Fourth Device)

<code># mdadm -G /dev/md5 -n 4 -a /dev/sdd</code>

12. Verify Filesystem Integrity and Resize

<code># e2fsck -f /dev/md5
# resize2fs /dev/md5</code>

13. Final RAID Information

<code># mdadm -D /dev/md5</code>

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