LPIC-2 Practice Question: Block Devices, Filesystems and Advanced Storage
Exhibit
# cat /proc/mdstat
Personalities : [raid1] [raid6] [raid5] [raid4]
md0 : active raid1 sdb1[0] sdc1[1]
2097152 blocks [2/2] [UU]
unused devices: <none>Refer to the exhibit. A system administrator wants to replace disk sdb1 in the RAID1 array. After physically removing sdb, which sequence of commands should be used?
⚠ Common exam trap
The trap here is that candidates often forget the `--run` step, assuming the array will automatically start after adding a new disk, or they mistakenly use `--grow` for adding a replacement disk instead of `--add`.
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 /dev/md0 --fail /dev/sdb1; mdadm /dev/md0 --remove /dev/sdb1; mdadm /dev/md0 --add /dev/sdd1; mdadm --manage /dev/md0 --run
After physically removing the failed disk (sdb), the administrator must first mark the device as failed using `--fail`, then remove it with `--remove`, add the new disk (sdd1) with `--add`, and finally run `--run` to ensure the array is activated if it was stopped or degraded. The `--run` flag is necessary because a RAID1 array with a missing device may not automatically start; this command forces the array to become active so the rebuild can begin. Note that the question does not involve filesystem extension; the focus is on the correct sequence for replacing a disk in a RAID array.
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 /dev/md0 --remove /dev/sdb1; mdadm /dev/md0 --add /dev/sdd1
Why it's wrong here
Missing the --fail step; the device must be marked as failed first.
- ✗
mdadm /dev/md0 --fail /dev/sdb1; mdadm /dev/md0 --remove /dev/sdb1; mdadm /dev/md0 --add /dev/sdd1
Why it's wrong here
Missing the --manage --run command to activate the new disk.
- ✗
mdadm /dev/md0 --fail /dev/sdb1; mdadm /dev/md0 --remove /dev/sdb1; mdadm --grow /dev/md0 --add /dev/sdd1; mdadm --manage /dev/md0 --run
Why it's wrong here
--grow is not needed for adding a replacement disk.
- ✓
mdadm /dev/md0 --fail /dev/sdb1; mdadm /dev/md0 --remove /dev/sdb1; mdadm /dev/md0 --add /dev/sdd1; mdadm --manage /dev/md0 --run
Why this is correct
Proper sequence: fail, remove, add, run.
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 LPIC-2 practice question is part of Courseiva's free LPI 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 LPIC-2 exam.