RAID 5 XOR Data Reconstruction
A forensic examiner is analyzing a RAID 5 array consisting of three disks. One disk has failed and is not available. The remaining two disks contain data and parity. Which technique can be used to reconstruct the missing disk's data and recover the original data?
Quick Answer
The answer is to use dd to image the two available disks and then perform a XOR operation on the data stripes to reconstruct the missing disk’s data. This works because RAID 5 distributes parity across all disks, and the XOR function is reversible: when one disk is missing, the data on the remaining disks can be combined via XOR to recover the lost stripe. On the CHFI exam, this tests your understanding of RAID forensics and the mathematical foundation of parity-based redundancy, often appearing in scenario-based questions where you must choose the correct reconstruction method over common traps like using RAID controllers or file carving alone. A key memory tip is to remember that XOR is the “undo” button for RAID 5—since parity is just the XOR of data stripes, applying XOR to the surviving disks yields the missing data.
⚠ Common exam trap
The CHFI exam often tests the misconception that RAID 5 can tolerate two disk failures or that simple imaging of surviving disks yields complete data without reconstruction, leading candidates to choose file carving or logical imaging 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
✓
Use dd to image the two disks, then perform a XOR operation on the data stripes to reconstruct the third disk's data
In a RAID 5 array with three disks, data and parity are striped across all disks. When one disk fails, the missing data can be reconstructed by performing an XOR operation on the corresponding stripes from the remaining two disks. This is because RAID 5 uses distributed parity where the parity block is the XOR of the data blocks in the same stripe, so XORing the surviving data and parity stripes recovers the lost data.
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 the failed disk and rebuild the array using the controller's rebuild function
Why it's wrong here
This requires the failed disk to be replaced and the array to be intact, not forensic analysis.
- ✓
Use dd to image the two disks, then perform a XOR operation on the data stripes to reconstruct the third disk's data
Why this is correct
XOR of data from two disks yields the missing data if parity is involved.
- ✗
Use FTK Imager to create a logical image of each disk and merge them
Why it's wrong here
FTK Imager does not reconstruct RAID stripes.
- ✗
Simply image the two disks and use file carving tools to extract files
Why it's wrong here
Without reconstruction, the data is incomplete and interleaved.
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.
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Same concept, more angles
1 more way this is tested on CHFI
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A forensic investigator analyzing a RAID 5 array of three disks notices that one disk has failed. Can the investigator still reconstruct the data?
hard- ✓ A.Yes, using the parity information from the remaining disks
- B.No, RAID 5 requires all disks to be present
- C.Yes, but only if the failed disk is the parity disk
- D.No, because RAID 5 does not support hot swapping
Why A: RAID 5 uses distributed parity across all disks in the array. When one disk fails, the data can be reconstructed by XORing the data and parity from the remaining disks. Since the parity is spread across all disks (not a dedicated parity disk), the investigator can rebuild the missing data as long as the remaining disks are functional.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CHFI practice question is part of Courseiva's free EC-Council 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 CHFI exam.