LFCS Storage Management Practice Question
An administrator is troubleshooting a server with a software RAID 1 array on /dev/md0. One disk, /dev/sdc, has failed and been replaced. The administrator runs `mdadm /dev/md0 --add /dev/sdc1` and sees the array rebuilding, but after a reboot the new disk is no longer part of the array. Which action should the administrator take to ensure the replacement disk is automatically reassembled into the array at boot?
⚠ Common exam trap
The trap here is assuming that adding a disk to a running array automatically updates the boot-time assembly configuration.
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 --detail --scan >> /etc/mdadm.conf` and update the initramfs.
Software RAID arrays are reassembled at boot from configuration stored in /etc/mdadm.conf and embedded in the initramfs. After adding a replacement disk, the administrator must regenerate that configuration and rebuild the initramfs so the new member is recognized. Growing the array, adding the component to fstab, or relying on a manual assemble command does not provide persistent boot-time assembly.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Add an entry for /dev/sdc1 to /etc/fstab with the `nofail` option.
Why it's wrong here
fstab controls filesystem mounting, not software RAID assembly. Adding the member disk to fstab would attempt to mount the raw RAID component as a filesystem, which is invalid and would likely fail or cause data corruption.
- ✗
Run `mdadm --grow /dev/md0 --raid-devices=2` to force the array to accept the new disk.
Why it's wrong here
The array already has two devices; --grow changes the number of devices in the array, which is used when adding a disk to a RAID 0 or expanding a RAID 5. It does not persist the new disk's membership and can corrupt the array if used incorrectly.
- ✗
Run `mdadm --assemble --scan` and rely on the kernel to remember the array across reboots.
Why it's wrong here
mdadm --assemble --scan is a one-time assembly command. The kernel does not persistently remember array membership across reboots; without an updated mdadm.conf or initramfs, the array may not include the replacement disk or may not assemble at all.
- ✓
Run `mdadm --detail --scan >> /etc/mdadm.conf` and update the initramfs.
Why this is correct
The mdadm.conf file tells the initramfs and mdadm which arrays to assemble at boot. Appending the current scan output records the new array UUID and device list, and updating the initramfs embeds that configuration so the array is reassembled with the replacement disk after a reboot.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Linux Foundation exam blueprint
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.