This EX200 practice question tests your understanding of configure local storage. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A production server runs RHEL 8 with a software RAID 5 array (/dev/md0) composed of three disks: /dev/sda, /dev/sdb, /dev/sdc. The array is used to store database files. The server experiences a disk failure on /dev/sdc. The admin replaces /dev/sdc with an identical disk and wants to rebuild the array. He runs: mdadm /dev/md0 --add /dev/sdc. The command completes without error, but the array shows a degraded state after several hours. What should the admin do next?
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 /dev/md0 to check the status and rebuild progress.
Option A is correct because after adding a replacement disk to a RAID 5 array, the rebuild process begins automatically but may take hours depending on disk size and I/O load. Running `mdadm --detail /dev/md0` allows the admin to check the current state, rebuild progress (e.g., percentage complete), and any errors that might have stalled the rebuild. This is the first diagnostic step to determine if the rebuild is still ongoing, has failed, or is degraded for another reason.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Run mdadm --detail /dev/md0 to check the status and rebuild progress.
Why this is correct
This shows the state of the array and any errors.
Related concept
Read the scenario before looking for a memorised answer.
✗
Rebuild will happen automatically; just wait longer.
Why it's wrong here
If it's been hours, something may be wrong; checking is prudent.
✗
Recreate the array using mdadm --create with the same parameters.
Why it's wrong here
Recreating destroys data; not needed if disk was added successfully.
✗
Format /dev/sdc with a filesystem before adding to the array.
Why it's wrong here
mdadm requires raw device, not formatted.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume the rebuild is always automatic and instantaneous, or they panic and choose destructive options like recreating the array, instead of first verifying the rebuild status with a simple diagnostic command.
Detailed technical explanation
How to think about this question
When a disk is added to a RAID 5 array with `mdadm --add`, the kernel initiates a recovery process that reads data from the remaining disks (sda, sdb) and writes parity and data to the new disk (sdc). The rebuild progress can be monitored via `/proc/mdstat` or `mdadm --detail`, which shows the status as 'recovery' with a percentage. In real-world scenarios, heavy I/O from the database can slow the rebuild, and the admin may need to adjust the `sync_speed_min` and `sync_speed_max` sysfs parameters to prioritize recovery.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the EX200 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Configure local storage — This question tests Configure local storage — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Run mdadm --detail /dev/md0 to check the status and rebuild progress. — Option A is correct because after adding a replacement disk to a RAID 5 array, the rebuild process begins automatically but may take hours depending on disk size and I/O load. Running `mdadm --detail /dev/md0` allows the admin to check the current state, rebuild progress (e.g., percentage complete), and any errors that might have stalled the rebuild. This is the first diagnostic step to determine if the rebuild is still ongoing, has failed, or is degraded for another reason.
What should I do if I get this EX200 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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