Data Recovery Case File · Portable Drives · Half a File Is Not Half Useless
What Survives an Interrupted Transfer Depends on What It Is
Her enquiry concerns one file rather than a drive. "While I was transferring a large file to it there was a power cut that interrupted the transfer. I haven't been able to access the file since, but my laptop does recognise the drive as a device." The drive is fine and a partial file exists — and whether that partial file is worth anything is not a question about recovery technique. It is a question about which format it is in.
| Media | External hard drive — single large file interrupted mid-transfer by mains failure; device enumerating normally; partial content present |
| Reported situation | Large file being transferred to the external drive · mains power interrupted during the transfer · file not accessible since · drive recognised by the host as a device · source status not stated · file required |
| Fault class | Incomplete write with directory inconsistency — partial content present; usability determined by file format rather than by recovery method |
| Equipment used | Source availability established before any work on the destination · written extent measured against the file's declared length · imaged write-blocked before any reconstruction · partial content assessed for structural usability by format · repair attempted per format where indicated |
The decode: the question before the technical one
What to establish first, because it may end this entirely: does the source still exist? She was transferring the file, not moving it — and unless the original was deleted afterwards, it is still wherever it came from. Checking takes a minute and it costs nothing.
What the interruption did: stopped a write partway. The directory entry was created with the file's intended length, and the content stops wherever the power did. So the record claims a size the content does not reach, which is why the system will not open it — the file is shorter than it says it is.
Now the part that decides the value, and it varies enormously by format.
Formats that survive truncation well: most video and audio. They are written as a sequence of independent chunks, decoded one after another, so a player reaching the end of the data simply stops. A video cut off at seventy per cent plays for seventy per cent — sometimes after a repair to fix the index, which for many formats lives at the end and will be missing.
Formats that survive partially: plain text and many documents. Text is readable to wherever it stops. Structured documents are frequently compressed archives internally, and a truncated one loses whatever came after the cut while earlier components remain extractable.
Formats that survive badly: compressed archives as a whole, and databases. An archive's index is typically at the end, so truncation removes the map to everything inside — though individual members can sometimes be extracted by locating their own headers.
Formats that survive not at all: anything encrypted as a single unit, and formats requiring a complete checksum before they will open.
Why that matters practically: the recovery is the same work in every case — the partial content is extracted and its true extent determined. What differs is whether the result is usable, and that should be established before anybody commits, not discovered afterwards.
What must not happen: no repair on the volume. A consistency check meeting an entry whose length exceeds its content resolves the disagreement by truncating the record — which discards the boundary information.
On the bench
Source availability was established before any work on the destination, a transfer being a copy rather than a move. Written extent was measured against the file's declared length — an interrupted write leaving a directory entry claiming the intended size while content stops where power did. Partial content was assessed for structural usability by format, sequentially-chunked media surviving truncation well while archive and database formats depending on trailing indexes generally do not.
The outcome
The source checked first, the written extent measured against the declared length, and partial content assessed for usability by format. 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: check whether the original still exists before anything else. Then know that a partial file's value depends on its format — video and audio play up to the cut, while archives lose their index and give up everything.
File interrupted by a power cut mid-transfer
Check the source first — you were copying rather than moving, so unless you deleted the original it's still where it came from, and that takes a minute to establish. If it really is gone, what you have is a partial file, and its worth depends almost entirely on format. Video and audio are written as sequences of independent chunks, so a truncated one plays up to the cut, sometimes after repairing an index that lives at the end. Text and many documents give up whatever preceded the cut. Compressed archives usually keep their index at the end, so truncation removes the map to everything inside. Don't run a repair on the volume.
Check the source — then call Oxford Data Recovery on 01865 593000; written extent measured against the declared length, partial content assessed for usability by format before you commit to anything.
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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.