Data Recovery Case File · Servers & RAID · RAID 5

Five healthy drives, one dead array: a RAID 5 recovered from images the customer made himself

"As a last resort," his enquiry began — but everything about it was the opposite of desperation. His server's RAID 5 logical volume had failed while all five member drives passed their health checks; he suspected two had overheated and shut themselves down at some point; and, decisively, he had imaged every drive immediately after removal and was offering us the images. It's the most professional opening position a RAID customer has ever handed us, and it shaped the whole job.

The enquiry

“The logical drive on my server has failed — five members in a RAID 5. All five drives appear healthy according to SMART; the controller can see them all. I suspect two may have overheated and shut themselves down but are still serviceable. I can drop off the physical drives, or provide a large drive containing the images I created straight after removing them.”

How an array dies while its disks live

His paradox — healthy disks, dead volume — is RAID 5's signature failure, and his overheating theory almost certainly explains it. A RAID controller doesn't judge drives on their long-term health; it judges them on answering right now. A drive that thermally shuts down mid-operation goes silent, the controller marks it failed and carries on degraded — and from that instant the dropped drive is frozen in the past, its contents growing staler with every write the survivors accept. When a second member later does the same, RAID 5's tolerance is spent and the volume fails outright — leaving five drives that all test perfectly, because they are perfect, wrapped around metadata that no longer tells one coherent story about who left when. The trap for any rebuilder is right there: assemble the array treating all five as equals and the stale members inject their outdated past into the reconstruction, corrupting exactly the files that changed most recently.

Working from his images — and honouring the drop order

His images were welcomed, and first audited: verified complete and hash-checked against the source drives on the TaskForce 2, because an image is only as good as its provenance — his passed, cleanly made. Reconstruction in Data Extractor then turned on the question his enquiry had intuited: who dropped out, and in what order? The members' own metadata answers it — each carries its record of array events — and the timeline resolved exactly as he'd suspected: two staggered departures. The array was therefore assembled the only correct way: from the four members that were current at the moment of final failure, with the first, stalest dropout excluded and its contribution recomputed from the survivors' parity — RAID 5's mathematics used one last time, on images, to rebuild the missing stripe of every row. The volume mounted from the virtual assembly; the server's file systems and data came out coherent, current to the final write.

Outcome

Full recovery, delivered — fittingly — back onto the large drive he'd supplied, alongside a written account of the drop sequence for his post-mortem. His imaging instinct deserves the last word: made before any rebuild attempt, those images froze the evidence and meant the original drives were never risked again. It's exactly what a lab does first, done before the lab was ever called. For everyone else running RAID 5 on veteran disks in a warm cupboard: the array that survives one silent dropout is already living on its last spare mistake — monitoring and airflow are cheaper than this page.

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.