Data Recovery Case File · Formatted & Logical Faults · The Checksum That Did Not Match
Data Error (Cyclic Redundancy Check): What It Means
His enquiry was four lines and quoted the message exactly, which is the most useful thing anyone can do. "My hard drive says: data not accessible. Data error (cyclic redundancy check). Is it possible to fix?" That error is one of the most precise a computer produces, and it is worth decoding properly because people read it as generic corruption when it is nothing of the kind. A cyclic redundancy check error means the drive returned data and knew it was wrong. Not missing, not unreadable in the sense of nothing arriving — arrived, checked, and failed. That distinction points at a specific layer, and it also identifies the one tool that should not be run next.
| Media | Hard drive reporting inaccessible data with cyclic redundancy check errors on access — nature and extent of underlying damage undetermined |
| Reported situation | Data inaccessible · consistent checksum failure reported on read attempts · no other symptoms specified · no repair attempted at enquiry |
| Fault class | Read-integrity failure — data returned failing its stored checksum, indicating media degradation or a compromised connection rather than filesystem damage |
| Equipment used | Cabling and connection eliminated first · Atola Insight Forensic surface and error-rate assessment · PC-3000 Express with Data Extractor imaging under per-sector timeouts · weak regions re-read on later passes · contents rebuilt from recovered sectors and verified |
The decode: what a checksum failure is, the free check, and the tool to avoid
What a cyclic redundancy check actually does: every sector written to a drive carries a small calculated value derived from its contents — a checksum. When the sector is read back, the value is recalculated and compared with the stored one. If they match, the data is intact. If they do not, something has changed between writing and reading, and the system reports a data error. So this message is not a vague complaint: it is a specific statement that the integrity check failed, which means the drive is being honest about returning something corrupted rather than silently handing over bad data. That honesty is a feature, and it is why the error exists.
What it points at: two possibilities, and the order matters. Most often the sector's magnetic recording has degraded — weak or damaged media, so what is read back no longer matches what was written. That is a media problem rather than a filesystem one, which is why filesystem tools do not resolve it. Less often, and worth eliminating because it is free, the data was corrupted in transit: a failing cable, a poor connection, a marginal port or an ageing enclosure can corrupt data between the drive and the computer, producing identical errors from a perfectly healthy drive. Trying a different cable and a different port, once, is genuinely worth doing before concluding anything.
The tool to avoid: and this is where these cases are usually lost. Faced with this error, Windows will suggest — and the internet will insist — running a disk check. That tool writes: it attempts to repair the filesystem, and on a drive returning checksum failures it will mark sectors bad, relocate what it can, discard what it cannot reconcile and modify structures throughout. On a genuinely degrading drive that is a sustained write and retry session on exactly the weakest ground, and it converts recoverable inconsistency into permanent loss. His question — is it possible to fix? — deserves the honest answer: the drive is not the thing to fix. The data is the thing to rescue, and rescuing it means not writing to the drive at all.
Why the outlook is often reasonable: a sector that fails its checksum on one attempt does not necessarily fail on the next. Drives and their controllers give up under timeouts that consumer software neither controls nor extends, and patient repeated reads under proper timeout control frequently return a clean copy of a sector that failed a dozen hurried attempts. That is the whole basis of the method: image once, healthy regions first, then revisit the difficult ground on its own terms.
On the bench
The connection was eliminated first, since a failing cable produces identical errors from a healthy drive and costs nothing to rule out. The Atola Insight Forensic then assessed surface condition and error rates directly, establishing whether the checksum failures were localised or widespread — the difference between a bounded problem and a drive in general decline. Imaging ran on the PC-3000 Express under Data Extractor with per-sector timeouts enforced, the healthy expanse captured at full speed first, and the failing regions revisited on later patient passes where repeated reads returned sectors that had failed their checks repeatedly. The contents were rebuilt from recovered sectors and verified by opening.
The outcome
The connection eliminated, the drive imaged under timeout control with weak regions re-read, and the contents rebuilt and verified. 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, for anyone seeing that message: a cyclic redundancy check error means data was returned and failed its stored checksum — the drive is telling you it knows what it handed over was wrong, which is honesty rather than vagueness; that points at degraded media, or occasionally at corruption in transit from a failing cable, so try a different cable and port once; and do not run a disk check, because it writes and retries on precisely the weakest ground. The drive is not the thing to fix.
Drive reporting a cyclic redundancy check error
Don't run a disk check, whatever Windows or the internet suggests. That message means a sector was read and failed its stored checksum — the drive knows what it returned was wrong — which points at degraded magnetic recording rather than a filesystem problem, and a filesystem repair tool addresses the wrong layer while writing to the drive and retrying on exactly the weakest ground. Do run one free test first: try a different cable and a different port, because data can also be corrupted in transit by a failing lead or a marginal connection, and that produces identical errors from a perfectly healthy drive. If the errors persist, stop using the drive, don't copy from it repeatedly, and don't let anything attempt to repair it. Sectors that fail a hurried read often succeed on patient repeated attempts under proper timeout control, which is why one careful imaging pass beats a hundred retries.
Try another cable once, then stop — call Glasgow Data Recovery on 0141 404 0294; surface and error rates measured, imaged under per-sector timeouts, weak sectors re-read patiently.
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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.