LFCS Storage Management Practice Question
A system administrator receives an alert that disk /dev/sda is predicted to fail soon. The server uses LVM, and /dev/sda is part of a volume group named vg_system. Which of the following is the best course of action to replace the failing disk without downtime?
⚠ Common exam trap
Many exam-takers confuse block-level cloning (dd) with LVM-aware migration (pvmove), assuming any copy tool can replace a disk in an LVM setup without understanding that LVM metadata and extent mapping must be handled correctly to avoid downtime or data corruption.
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
✓
Use pvmove to move physical extents to another disk, then remove the old disk.
Pvmove relocates physical extents from /dev/sda to another physical volume in the same volume group while the filesystem remains online and accessible. This allows the failing disk to be removed from vg_system without any downtime, preserving LVM metadata and data integrity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use dd to clone /dev/sda to a new disk and then replace.
Why it's wrong here
dd clones the whole block device, so it cannot be done while /dev/sda is mounted and in use, forcing downtime. It is tempting because dd is the standard tool for duplicating disks, and it would be correct for a single unmounted disk with no volume manager, but LVM offers pvmove for live migration.
- ✗
Use ddrescue to copy data, then replace the disk.
Why it's wrong here
ddrescue copies block data from the failing disk, but the source must be offline or read-only, so the volume group cannot stay active. It is tempting because ddrescue handles bad sectors well, and it would be correct for recovering a standalone failing disk, but LVM's pvmove migrates extents without downtime.
- ✗
Remove /dev/sda from the volume group and add a new disk.
Why it's wrong here
Removing /dev/sda from vg_system with vgreduce discards the logical volumes' data unless extents are first migrated, and the physical volume cannot simply be dropped while in use. It is tempting because vgreduce removes a PV, and it would be correct after pvmove has evacuated all extents to another disk.
- ✓
Use pvmove to move physical extents to another disk, then remove the old disk.
Why this is correct
pvmove relocates the physical extents residing on the failing physical volume to another disk in vg_system while the volume group stays online. The old disk can then be removed with vgreduce and pvremove, replacing it without downtime.
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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.