Imaging an Unstable Drive with Read Errors
At 14:05 on 12 August, a laptop is seized from a suspect’s apartment. The internal 4 TB SATA hard drive is removed and connected through a hardware write blocker to a forensic workstation. The drive makes intermittent clicking sounds. The examiner starts a physical image to a 4 TB raw file on a 6 TB evidence drive using a hardware imager. At 63%, the imager reports read errors and stops advancing; the source drive remains detected. The case involves a ransomware demand and a spreadsheet alleged to contain victim identities. The examiner has a second 4 TB drive, a ddrescue workstation, and an evidence USB with a known-good hash. The lab policy requires verified images and a written deviation record. The suspect’s attorney has requested a copy of the image. The initial imaging attempt produced a partial raw file of 2.52 TB.
1. What should the examiner do before resuming acquisition, and why?
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The examiner should stop repeatedly power-cycling the unstable drive. Each spin-up risks further mechanical damage and can destroy the very sectors needed for the case. First, preserve the partial 2.52 TB raw file as evidence: record its exact size, hash it, and preserve the imager logs and error messages. Do not overwrite or delete it.
Next, use a fresh destination and a tool that records error locations, such as ddrescue with a mapfile. A sensible sequence is a first pass that skips bad areas quickly, then retries on error regions, then a trim or scrape pass if appropriate. The examiner should document the write blocker, cabling, tool versions, commands, and power-on time. If the drive continues to click or becomes undetected, professional recovery may be preferable to further lab attempts. The goal is not to force a perfect image at any cost; it is to recover as much data as possible while preserving an accurate record of what could not be read.
2. How should bad sectors and the partial image be documented and verified?
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Because the source cannot be read completely, a source-to-image hash match may be impossible. The examiner should not claim a full bit-for-bit verification. Instead, verify the acquired image by hashing it, then hash a working copy or a second image and compare those values. The ddrescue mapfile or imager error log should be preserved and summarized in the report, including unreadable sector ranges and counts.
The partial raw file should be hashed and described as a partial acquisition, not as a complete image. If the examiner later creates a fuller image, the relationship between the partial and final images should be documented. A mismatch caused by skipped bad sectors is expected and is not evidence of tampering, but the report must explain why. The deviation record should state the lab policy, the exception, the tools used, and the examiner’s rationale. Verification of individual known files can supplement, but not replace, the hash and error-map documentation.
3. How should the examiner respond to the defense request for a copy of the image?
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The examiner should follow lab policy and counsel’s direction, but the technical response is straightforward: provide a verified working copy, not the original evidence drive. The copy should be hash-verified, logged, and transferred with a chain-of-custody record. The examiner should also provide the error map or a clear explanation that the image contains unreadable sectors, so the defense expert does not misinterpret a hash mismatch or missing data as tampering.
If the image is partial, the examiner should say so explicitly and explain what ranges are affected. Any protective order, redaction, or disclosure limitation is for counsel to decide; the examiner should not alter the image. The examiner can offer the same tools and documentation needed to reproduce the acquisition and verification. This transparency strengthens the foundation and avoids later claims that the laboratory concealed defects in the image.