The most likely cause of an I/O error during disk acquisition is that the source disk has bad sectors. This occurs because physical damage or degradation of the storage media prevents the read head from reliably retrieving data, triggering an I/O error at the operating system or device driver level when tools like dd, FTK Imager, or EnCase attempt to read the affected areas. On the CHFI exam, this question tests your understanding of hardware-level acquisition challenges versus logical issues like file system corruption, which typically produce different error messages. A common trap is confusing I/O errors with permission or format errors, but remember that bad sectors are a physical, not logical, problem. Memory tip: “Bad sectors block reads—I/O errors mean the disk bleeds.”
CHFI Evidence Acquisition and Duplication Practice Question
This CHFI practice question tests your understanding of evidence acquisition and duplication. 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.
Exhibit
Refer to the exhibit.
[root@forensics ~]# dc3dd if=/dev/sda of=/evidence/sda.img hash=sha256 log=/evidence/log.txt
Output:
Fatal error: Input/output error while reading /dev/sda
The command used to acquire a disk image resulted in an I/O 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The source disk has bad sectors
When a disk imaging tool (e.g., dd, FTK Imager, EnCase) encounters an I/O error during acquisition, the most common cause is physical damage or degradation of the source media, specifically bad sectors. Bad sectors prevent the read head from reliably retrieving data, triggering an I/O error at the operating system or device driver level. This is distinct from logical errors like file system corruption, which typically produce different error messages.
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 source disk has bad sectors
Why this is correct
Bad sectors cause read errors.
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 output file already exists and is being overwritten
Why it's wrong here
This would not cause an I/O error.
✗
The target directory does not have write permissions
Why it's wrong here
This would cause a permission error.
✗
The target drive is full
Why it's wrong here
A full drive would cause a no space error.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse an I/O error (a hardware-level read failure) with logical or permission-based errors, mistakenly attributing the error to the output destination rather than the source media.
Detailed technical explanation
How to think about this question
Under the hood, a disk I/O error typically corresponds to a SCSI sense key of 'Medium Error' (0x03) or 'Hardware Error' (0x04), often with an additional sense code indicating 'Unrecovered Read Error' (0x11,0x00). Forensic tools like dd with conv=noerror,sync can skip bad sectors and continue imaging, but the I/O error still occurs at the block device level. In real-world acquisitions, a single bad sector can halt the entire process if the tool is not configured to handle errors, potentially losing evidence from surrounding good sectors.
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 CHFI 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CHFI question in full detail.
Evidence Acquisition and Duplication — This question tests Evidence Acquisition and Duplication — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The source disk has bad sectors — When a disk imaging tool (e.g., dd, FTK Imager, EnCase) encounters an I/O error during acquisition, the most common cause is physical damage or degradation of the source media, specifically bad sectors. Bad sectors prevent the read head from reliably retrieving data, triggering an I/O error at the operating system or device driver level. This is distinct from logical errors like file system corruption, which typically produce different error messages.
What should I do if I get this CHFI 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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Question Discussion
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