- A
The array is in a degraded state and the recovery is waiting for the resync to start, but the event count is zero; the array may need to be forced to start recovery.
Event count 0 and recovery stuck at 0% suggests the array isn't initiating resync; sometimes a 'mdadm --assemble --force' or 'mdadm --run' is needed.
- B
The recovery is complete because the data is already synchronized.
Why wrong: The status shows recovery = 0.0% and array is [_U] meaning only one device is active.
- C
The device /dev/sdb1 was not properly removed; it still holds old metadata that conflicts.
Why wrong: The mdadm --remove succeeded, and re-add shows it as a new device (number 2).
- D
The new disk /dev/sdb1 has a different size than the original, causing the recovery to stall.
Why wrong: The fdisk output shows /dev/sdb1 size 10G, but the md array is only 1G. However, the mdadm --add might fail if partition sizes don't match; but here it was re-added.
EX200 Configure local storage Practice Question
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.
Refer to the exhibit. After re-adding the disk, the recovery process shows 0% progress and remains at 0. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
The array is in a degraded state and the recovery is waiting for the resync to start, but the event count is zero; the array may need to be forced to start recovery.
Option A is correct because when a disk is re-added to a Linux software RAID (mdadm) array, the recovery process may stall at 0% if the array's event count is zero. This occurs when the array was created with a missing disk and the metadata on the re-added disk does not match the array's current event counter, preventing the automatic resync from starting. The recovery waits for a resync trigger, but without a proper event count, it remains stuck; forcing recovery with `mdadm --assemble --force` or `mdadm --manage /dev/mdX --add /dev/sdb1` can initiate the resync.
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.
- ✓
The array is in a degraded state and the recovery is waiting for the resync to start, but the event count is zero; the array may need to be forced to start recovery.
Why this is correct
Event count 0 and recovery stuck at 0% suggests the array isn't initiating resync; sometimes a 'mdadm --assemble --force' or 'mdadm --run' is needed.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The recovery is complete because the data is already synchronized.
Why it's wrong here
The status shows recovery = 0.0% and array is [_U] meaning only one device is active.
- ✗
The device /dev/sdb1 was not properly removed; it still holds old metadata that conflicts.
Why it's wrong here
The mdadm --remove succeeded, and re-add shows it as a new device (number 2).
- ✗
The new disk /dev/sdb1 has a different size than the original, causing the recovery to stall.
Why it's wrong here
The fdisk output shows /dev/sdb1 size 10G, but the md array is only 1G. However, the mdadm --add might fail if partition sizes don't match; but here it was re-added.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common mistake on the RHCSA exam is to think that a stalled recovery at 0% means the disk is faulty or the array is degraded, when in fact it is a metadata event count mismatch that prevents the automatic resync from initiating.
Trap categories for this question
Command / output trap
The status shows recovery = 0.0% and array is [_U] meaning only one device is active.
Detailed technical explanation
How to think about this question
In Linux md RAID, the event count is a monotonically increasing number stored in each disk's superblock, used to track the most recent write to the array. When a disk is re-added, mdadm compares its event count to the array's current count; if the disk's count is lower, the array initiates a resync to update it. However, if the event count is zero (e.g., from a newly created array or a disk that was never part of the active set), the resync may not start automatically because the kernel sees no delta to resolve, requiring manual intervention with `mdadm --manage /dev/md0 --add /dev/sdb1` or a forced reassemble to trigger the 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.
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.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this EX200 question test?
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: The array is in a degraded state and the recovery is waiting for the resync to start, but the event count is zero; the array may need to be forced to start recovery. — Option A is correct because when a disk is re-added to a Linux software RAID (mdadm) array, the recovery process may stall at 0% if the array's event count is zero. This occurs when the array was created with a missing disk and the metadata on the re-added disk does not match the array's current event counter, preventing the automatic resync from starting. The recovery waits for a resync trigger, but without a proper event count, it remains stuck; forcing recovery with `mdadm --assemble --force` or `mdadm --manage /dev/mdX --add /dev/sdb1` can initiate the resync.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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