LPIC-2 Practice Question: Block Devices, Filesystems and Advanced Storage
A Linux administrator is managing a database server running on CentOS 7 that uses ext4 filesystems on LVM. The server has three physical volumes: /dev/sda (200GB), /dev/sdb (200GB), and /dev/sdc (200GB) all in volume group 'vg_db'. The logical volume 'lv_data' (400GB) is used for database files. Recently, the DBA reports that database writes are slower than expected. Iostat shows high average wait times (>100ms) on /dev/sdc but normal on /dev/sda and /dev/sdb. The LVM stripes data across all three PVs with a stripe size of 64KB. Which action should the administrator take to improve performance?
⚠ Common exam trap
Many exam-takers think increasing stripe size or reducing stripe count will improve performance, but they overlook that a single failing or slow physical volume in a striped logical volume creates a synchronous bottleneck that cannot be mitigated by tuning stripe parameters alone.
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
✓
Replace /dev/sdc with a new disk and restore the mirror or restripe.
The high average wait time on /dev/sdc indicates that this specific physical volume is a performance bottleneck, likely due to hardware failure or degradation. Since the logical volume 'lv_data' stripes data across all three PVs, the overall write performance is limited by the slowest device in the stripe set. Replacing /dev/sdc with a new disk and restoring the stripe (e.g., using pvmove to relocate extents and then replacing the device) eliminates the bottleneck and restores balanced I/O across all PVs.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Replace /dev/sdc with a new disk and restore the mirror or restripe.
Why this is correct
The slow disk is the bottleneck; replacing it resolves the issue.
- ✗
Convert lv_data to linear mapping on /dev/sda and /dev/sdb only.
Why it's wrong here
This loses the benefit of striping and may not improve performance.
- ✗
Increase the stripe size to 256KB to reduce I/O overhead.
Why it's wrong here
This may not address the slow disk; the issue is at the device level.
- ✗
Remove /dev/sdc from the volume group and reduce the stripe count to 2.
Why it's wrong here
Reducing stripes reduces parallelism, may hurt performance further.
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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.