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PDR / Casebook / A Redundancy Check Halted Every Copy

Missing or corrupt files · job record · PLY-2025-0311

Every Large Copy Stopped on the Same Message.

The Toshiba had sat in its dock on an office shelf for years when the power failed. Copying stopped working from then on. A few files first, then whole folders, always halting at cyclic redundancy check. A new lead made no difference; nor did carrying it out to the works and trying the laptop there; and I had Windows checking the thing two nights in a row and it hadn't finished either morning. What sat on the disk was thirty years of shop drawings belonging to a fabricator at Cattedown in Plymouth: every staircase and every handrail since I started up.

The customer checked and agreed No names published

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Why it happens.

That message carries less meaning than people give it. All it states is that a block arrived back from the drive without matching the check value held alongside it. Nothing more. Two unrelated faults finish in the same place — a filesystem whose bookkeeping has slipped on hardware in perfect order, or a surface that has lost the ability to keep what was written to it. Treating the second as the first makes it worse, so guessing gets expensive fast. Faced with a weak patch, Windows simply repeats the request, over and over, until a sector replies or the drive stops responding altogether. He had already spent two nights on that.

The kit this job called for.

How the job runs →
The kitWhat it did hereWhy we keep it
DeepSpar Disk Imager 4Copied the Toshiba under a retry ceiling, marking the poor ground and carrying onScores every head before it starts, works one surface at a time, and holds resets, timeouts and power in check
R-Studio TechnicianRebuilt the volume off the image instead of off the driveReads nearly every file system, and rebuilds RAID sets from images
ACE Lab PC-3000 ExpressRead the firmware before touching a sector: how the attributes were trending, what the grown defect list held, and two sessions that had run all nightDrops the disk into its maker's service mode, out of reach over plain ATA

How it ran.

01

Ask the drive first, because it keeps records

No sector was read before the firmware had been questioned, and its answer was plain. The reallocated count stood high and was still going up, with more sectors waiting their turn behind it. Two long sessions in the power-on log matched, almost hour for hour, the two nights he had spent scanning. So the fault lay in the surface rather than in the bookkeeping.

02

Retries cost time, so put a ceiling on them

The limits were fixed before imaging began: short timeouts, a capped number of tries, and any band that resisted got logged, passed over and left where it was. Those passed-over bands were given one brief run at the very end. Arithmetic, not obstinacy. An hour spent on a single bad sector can cost you the thousand sound ones sitting behind it.

03

Shut the drive down, then work on the copy

Once the copy was safely written the Toshiba went off and stayed off. The copy came out better than the counters had promised. Nothing was missing from the folder tree, and the losses clustered in a single band beneath a set of scanned sheets. Every absent sheet was named in the report by its own filename, which left him a list to take to the plan chest rather than an apology.

How it ended up.

While still on the telephone he had named the folder that came ahead of all the others: staircases and balustrades on buildings that people use every day. That folder was opened and read before anybody raised the invoice. A new disk carried the archive home, whole apart from the sheets set out in the report. Two of those exist on paper at the works and can be drawn again. The others belong to jobs finished before he took over the firm, and that paper went out years ago.

In short: A CRC error is a drive telling you the truth. Take the one clean copy it will still allow you, and then stop asking it for more.

Seeing the same thing?

Leave it switched off and post it in. Nothing happens until the diagnosis, which lists what can still be read and what cannot.

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