Data Recovery Case File · Cameras, Drones & Cards · Reading Involved Writing
An Unclean Removal Marks a Volume Dirty, and the Host Reports That as Corruption
His enquiry describes an operation that ought to have been harmless. Video being copied from a card to a laptop when "the laptop's battery died", and on restarting, "it said that all the files saved on the card were corrupted" — with five particular videos wanted. Copying is a read, and a read should not damage anything, which makes the outcome look worse than it is: what the host is reporting is a flag it set itself.
| Media | Memory card mounted for a copy operation interrupted by host power loss — host subsequently reporting all content as corrupted; five specific video files sought |
| Reported situation | Video files being copied from a memory card to a laptop · laptop losing power during the transfer · card remaining inserted through the power loss · host reporting all card content as corrupted on restart · five particular files required |
| Fault class | Volume marked as not cleanly unmounted following interrupted access — filesystem structures likely intact with a dirty flag set; video content unaffected by a read operation |
| Equipment used | Host corruption report distinguished from actual structural damage · no repair, check or format permitted on the card · imaged write-blocked at the block level before any interpretation · filesystem state examined for clean-unmount flags separately from structural integrity · video streams carved by signature and the required files identified by duration and timestamp |
The decode: why a read operation left the card flagged
Why mounting a card is not a read-only act: the system records that it is in use. When a volume is mounted, a flag is written marking it as open, and that flag is cleared when it is unmounted properly.
What happens when power fails before that: the flag stays set. The card retains a marker saying it was mounted and never cleanly closed.
What the system does on seeing it next: assumes the worst. A volume flagged as unclean is treated as potentially inconsistent, and many systems report that as corruption regardless of the actual state.
Why the wording is misleading rather than wrong: it describes a possibility. The system genuinely does not know whether writes were in progress, so it reports the uncertainty as damage.
Why in his case there almost certainly were none: he was copying from the card. A copy reads from the source and writes to the destination, so the card was being read and the laptop was being written to.
What that means for the videos: they were not touched. Content being read is not modified, and the files on the card are as they were before the transfer began.
What may genuinely have been affected: small metadata updates. Systems update access times and similar records even during reads, which is what could have been interrupted.
Why that is a trivial inconsistency: it affects records rather than content. A partially updated timestamp does not damage a video file.
Why the card must not be repaired or checked: that would write. Accepting an offer to fix the volume rewrites structures to clear the flag, and on a card of unknown condition that write may not complete.
What is worth checking about the destination as well: partial copies. Files already transferred to the laptop before the power loss may be complete and usable, and any file copied fully is one fewer to recover.
On the bench
The host corruption report was distinguished from actual structural damage — mounting a volume writing a flag marking it open, cleared only on proper unmount, so power loss leaves that flag set and the system treats the volume as potentially inconsistent, frequently reporting it as corruption. A copy reads from the source and writes to the destination, so card content was not modified. Filesystem state was examined for clean-unmount flags separately from structural integrity.
The outcome
The corruption report distinguished from structural damage, no repair permitted on the card, and video streams carved with the required files identified. Free assessment, one fixed written figure including VAT; on cards where content has been deleted or overwritten, the figure is payable upfront. The decode: you were reading from the card and writing to the laptop. The card kept a flag saying it was mounted and never closed properly — and your system is reporting that flag, not your videos.
A card reported corrupt after a power loss
Refuse any offer to fix, check or format it — that rewrites structures to clear the flag, and on a card of unknown condition the write may not complete. Understand what's being reported: mounting a volume writes a marker saying it's open, cleared only on proper ejection, so an interrupted session leaves it set and the system treats the volume as suspect. Since you were copying from the card, its content was being read rather than written. Check what already reached the laptop.
Don't let anything fix it — call Cambridge Data Recovery on 01223 655015; the report distinguished from actual damage, imaged write-blocked, streams carved and your required files identified.
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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.