LFCS Storage Management Practice Question
A disk in a RAID5 array fails. The array is assembled using mdadm. Which is the correct procedure to replace the failed disk with a new one?
⚠ Common exam trap
Many candidates assume a hot-swap or a single '--add' command is sufficient, but the LFCS exam expects the full three-step procedure to ensure the array state is properly managed before introducing a new disk.
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
✓
Run 'mdadm --fail /dev/md0 /dev/sdb', then 'mdadm --remove /dev/md0 /dev/sdb', then physically replace, then 'mdadm --add /dev/md0 /dev/sdb'.
It follows the proper mdadm procedure for replacing a failed disk in a RAID5 array. First, you must mark the disk as failed with 'mdadm --fail' to ensure the array stops using it, then remove it with 'mdadm --remove' to detach it from the array. After physically replacing the disk, you add the new disk with 'mdadm --add', which triggers a rebuild of the array from the remaining disks' parity data.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Physically replace the disk, then run 'mdadm --add /dev/md0 /dev/sdb'.
Why it's wrong here
The failed disk must first be removed from the array.
- ✗
Run 'mdadm --replace /dev/md0 /dev/sdb' with the new disk path.
Why it's wrong here
The --replace option does not exist; use --fail, --remove, --add.
- ✓
Run 'mdadm --fail /dev/md0 /dev/sdb', then 'mdadm --remove /dev/md0 /dev/sdb', then physically replace, then 'mdadm --add /dev/md0 /dev/sdb'.
Why this is correct
Correct step-by-step procedure.
- ✗
Hot-swap the disk and the array automatically recovers.
Why it's wrong here
Automatic recovery may occur if hot-swap is supported, but manual steps are still recommended and often required.
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
This LFCS practice question is part of Courseiva's free Linux Foundation certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the LFCS exam.