LFCS RAID 5 Practice Question
A Linux administrator needs to create a RAID 5 array using three disks: /dev/sdb, /dev/sdc, and /dev/sdd, each 2TB. The administrator wants to ensure the array can be reassembled automatically after a reboot. Which command should be used to create the array?
⚠ Common exam trap
The trap is that candidates may choose `--metadata=0.90` (option A) because it is older and familiar, but they overlook that metadata version 0.90 has a 2 TiB limit per device and total array size. While each 2TB disk is under 2 TiB, a 3-disk RAID 5 array would exceed the total 2 TiB limit, causing the creation to fail. Metadata version 1.2 is required for arrays larger than 2 TiB and also supports automatic reassembly after reboot.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sdb /dev/sdc /dev/sdd --metadata=1.2
It uses `--metadata=1.2`, which stores the superblock at a standard 4 KiB offset from the start of each device, enabling the kernel to automatically discover and assemble the RAID array on reboot without manual intervention. RAID 5 with three disks provides striping with distributed parity, offering a balance of performance and redundancy.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sdb /dev/sdc /dev/sdd --metadata=0.90
Why it's wrong here
Metadata 0.90 has a 2TB total limit; each disk 2TB would exceed.
- ✗
mdadm --create /dev/md0 --level=1 --raid-devices=3 /dev/sdb /dev/sdc /dev/sdd
Why it's wrong here
This creates RAID 1 (mirror), not RAID 5.
- ✗
mdadm --create /dev/md0 --level=0 --raid-devices=3 /dev/sdb /dev/sdc /dev/sdd
Why it's wrong here
This creates RAID 0, not RAID 5.
- ✓
mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sdb /dev/sdc /dev/sdd --metadata=1.2
Why this is correct
Correct for RAID 5 with metadata 1.2, supporting large disks and auto-assembly.
Visual reference
Quick reference
RAID Level Comparison
| RAID Level | Min Disks | Fault Tolerance | Read | Write | Usable Capacity |
|---|---|---|---|---|---|
| RAID 0 | 2 | None | Excellent | Excellent | 100% |
| RAID 1 | 2 | 1 disk | Good | Moderate | 50% |
| RAID 5 | 3 | 1 disk | Good | Moderate | 67–94% |
| RAID 6 | 4 | 2 disks | Good | Lower | 50–88% |
| RAID 10 | 4 | 1 disk per mirror | Excellent | Good | 50% |
RAID is not a backup strategy — it protects against disk failure but not against accidental deletion, ransomware, or site-level events.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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