Data Recovery Case File · Formatted & Logical Faults · And Then It Stopped, Which Helped
It Began Overwriting the Disk That Held the File It Was Reading
Her enquiry describes a mistake that interrupted itself. Writing an installation image to a memory stick, she "accidentally targeted a hard drive I use. The image was on the hard drive, so it seemingly overwrote itself, and after that point failed and stopped writing. The hard drive still works physically." The tool destroyed its own source and then could not continue — which sounds worse than it is, because failing early is what bounded the damage.
| Media | Hard drive incorrectly selected as the destination for a disk image write — source image resident on the same drive; write failing partway and terminating |
| Reported situation | Installation image being written to removable media · hard drive selected as destination in error · source image resident on that hard drive · write commencing and overwriting the source · write failing and terminating · drive physically functional · contents required |
| Fault class | Bounded sequential overwrite from sector zero — partition and filesystem structures replaced; content beyond the written extent unaffected |
| Equipment used | Written extent measured against capacity before any conclusion · no further writing permitted · imaged write-blocked before any reconstruction · partition and filesystem structures located from surviving copies beyond the written region · files validated by opening |
The decode: where it wrote, how far it got, and why that stopped it
What a disk image writer does: writes a complete image to a device sequentially, starting at the very first sector. It does not create a file on the destination — it replaces the destination, which is the entire point of the tool and the reason selecting the wrong one is so consequential.
Why it destroyed its own source: the image file was stored on the drive it was writing to. The tool read from the beginning of that file while writing over the beginning of the disk, and the two collided — once the write reached the region holding the source, the source stopped being readable and the operation failed.
Why that failure is the best thing that happened: it stopped. The written extent is bounded by however far it got before destroying what it was reading, which on a drive of any size is a small fraction. Had the image been on a different device, the write would have completed and covered the whole quantity.
What was actually written over, and this is the specific loss: the beginning of the drive. The partition table went first, then the start of the filesystem — the structures describing where everything lives. Those occupy a small region and they are exactly what the tool overwrote.
Why the content is unaffected: files occupy the vast remainder of the drive, well beyond anything the write reached. They were never visited, and they sit where they always did — undescribed rather than removed.
Why the position is recoverable: filesystems keep backup copies of their key structures away from the primary set, and partition information is reconstructable from the volumes themselves. Both live beyond the written region, which is why an overwrite confined to the start of a drive is among the more tractable accidents here.
What must not happen: nothing further written, and no acceptance of any offer to initialise or format. The system will now see a drive with no readable partition table and will offer to prepare it, which would write over the region a reconstruction reads.
The prevention, and it is one habit: disconnect everything except the target before running such a tool, and never keep the source image on a drive that appears in the destination list.
On the bench
Written extent was measured against capacity before any conclusion — a disk image writer replacing a destination sequentially from the first sector, so the source residing on that destination caused the write to destroy what it was reading and terminate, bounding the damage to a small fraction of capacity. No further writing was permitted, the system now offering to initialise a drive with no readable partition table. Structures were located from surviving copies beyond the written region.
The outcome
The written extent measured before any conclusion, no further writing permitted, and the structures recovered from copies beyond the overwritten region. Free assessment, one fixed written figure including VAT; where a drive has to be opened, 50% of parts and labour is payable upfront with the balance only on success — otherwise no recovery, no fee. The decode: it failing early is what saved you. The tool writes sequentially from the first sector, so it destroyed the source it was reading and stopped — leaving the damage confined to the beginning of the drive, where the structures live rather than the content.
Disk writing tool aimed at the wrong device
Refuse any offer to initialise or format the drive — the system will now see no readable partition table and will suggest preparing it, which writes over exactly the region a reconstruction needs. Take some encouragement from how it failed. These tools replace a destination sequentially from the very first sector, so with the source image sitting on that same drive, the write destroyed what it was reading and stopped, bounding the damage to a small fraction of the capacity. What went is the beginning: the partition table and the start of the filesystem. Your files occupy the remainder and were never reached. Next time, disconnect everything except the target.
Refuse the initialise prompt — call Oxford Data Recovery on 01865 593000; written extent measured against capacity, imaged before any reconstruction, structures recovered from copies beyond the overwritten region.
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Our case files are drawn from genuine enquiries received by our laboratory over the past ten years, anonymised to protect client confidentiality. Each one describes the diagnostic and recovery procedure our engineers apply to that fault, using the equipment listed.