LVM Filter: Why pvcreate Fails with 'Device Not Found'
This EX200 practice question tests your understanding of configure local storage. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Exhibit
# cat /etc/lvm/lvm.conf | grep -A5 'filter ='
# By default we accept every block device:
filter = [ "a|.*|" ]
# pvcreate /dev/sdb
Device /dev/sdb excluded by a filter.
# lvmdiskscan
/dev/sda1 [ 17.15 GiB]
/dev/sda2 [ 2.00 GiB]
/dev/sdb [ 10.00 GiB]
0 disks
3 partitions
0 LVM physical volumes
0 LVM logical volumes
# ls -l /dev/sdb
brw-rw----. 1 root disk 8, 16 Nov 25 10:00 /dev/sdb
Refer to the exhibit. An administrator tries to initialize /dev/sdb as an LVM physical volume but gets an error. 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.
Exhibit
# cat /etc/lvm/lvm.conf | grep -A5 'filter ='
# By default we accept every block device:
filter = [ "a|.*|" ]
# pvcreate /dev/sdb
Device /dev/sdb excluded by a filter.
# lvmdiskscan
/dev/sda1 [ 17.15 GiB]
/dev/sda2 [ 2.00 GiB]
/dev/sdb [ 10.00 GiB]
0 disks
3 partitions
0 LVM physical volumes
0 LVM logical volumes
# ls -l /dev/sdb
brw-rw----. 1 root disk 8, 16 Nov 25 10:00 /dev/sdb
A
The /etc/lvm/lvm.conf filter is set to exclude /dev/sdb.
The filter in /etc/lvm/lvm.conf can exclude devices from LVM recognition. If /dev/sdb matches a reject pattern, pvcreate will fail with an error indicating the device is ignored or not found, even though it exists.
B
The device /dev/sdb has a filesystem on it.
Why wrong: If /dev/sdb had a filesystem, pvcreate would still succeed (though it would warn about overwriting). The error described is about initialization failure, not an existing filesystem.
C
The device /dev/sdb does not exist.
Why wrong: The device /dev/sdb is assumed to exist since the administrator is trying to initialize it. The error is not about device not found.
D
The device /dev/sdb is already in use by another volume group.
Why wrong: If /dev/sdb were already in use by another volume group, pvcreate would show a message indicating it's already a PV. The error in the scenario is different.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The /etc/lvm/lvm.conf filter is set to exclude /dev/sdb.
The error when initializing /dev/sdb as an LVM physical volume is most likely caused by the filter in /etc/lvm/lvm.conf excluding the device. The filter uses regular expressions to accept or reject block devices; if /dev/sdb matches a reject pattern (e.g., `filter = [ "r|/dev/sdb|" ]`), `pvcreate` will fail with a message like 'Device /dev/sdb not found (or ignored by filtering)'. This is a common configuration issue in environments where administrators restrict LVM to specific disks.
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 /etc/lvm/lvm.conf filter is set to exclude /dev/sdb.
Why this is correct
The filter in /etc/lvm/lvm.conf can exclude devices from LVM recognition. If /dev/sdb matches a reject pattern, pvcreate will fail with an error indicating the device is ignored or not found, even though it exists.
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 device /dev/sdb has a filesystem on it.
Why it's wrong here
If /dev/sdb had a filesystem, pvcreate would still succeed (though it would warn about overwriting). The error described is about initialization failure, not an existing filesystem.
✗
The device /dev/sdb does not exist.
Why it's wrong here
The device /dev/sdb is assumed to exist since the administrator is trying to initialize it. The error is not about device not found.
✗
The device /dev/sdb is already in use by another volume group.
Why it's wrong here
If /dev/sdb were already in use by another volume group, pvcreate would show a message indicating it's already a PV. The error in the scenario is different.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Red Hat often tests the LVM filter configuration as a hidden cause of 'device not found' errors, leading candidates to incorrectly suspect missing devices or filesystem conflicts instead of checking the lvm.conf filter.
Trap categories for this question
Command / output trap
If /dev/sdb were already in use by another volume group, pvcreate would show a message indicating it's already a PV. The error in the scenario is different.
Scenario analysis trap
If /dev/sdb were already in use by another volume group, pvcreate would show a message indicating it's already a PV. The error in the scenario is different.
Detailed technical explanation
How to think about this question
The LVM filter in /etc/lvm/lvm.conf is evaluated during `pvcreate`, `vgscan`, and other LVM commands; it uses a list of patterns where `a/.../` means accept and `r/.../` means reject. A common real-world scenario is when system administrators restrict LVM to specific multipath devices (e.g., `/dev/mapper/`) to avoid accidentally using local disks, and a misconfigured filter can silently ignore a device. The `pvcreate` command checks the filter before probing the device, so even if the device exists and is writable, it will be skipped if rejected.
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: The /etc/lvm/lvm.conf filter is set to exclude /dev/sdb. — The error when initializing /dev/sdb as an LVM physical volume is most likely caused by the filter in /etc/lvm/lvm.conf excluding the device. The filter uses regular expressions to accept or reject block devices; if /dev/sdb matches a reject pattern (e.g., `filter = [ "r|/dev/sdb|" ]`), `pvcreate` will fail with a message like 'Device /dev/sdb not found (or ignored by filtering)'. This is a common configuration issue in environments where administrators restrict LVM to specific disks.
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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