A mirror is supposed to mean a spare copy. This one had two copies that had aged identically, developed bad sectors in parallel, and would not have survived the rebuild the owner was about to start.
An accountancy practice ran its file share on a two-disk mirror in a small server. One disk had been reported as failed by the controller some weeks earlier and nobody had acted; the volume still mounted, so the problem stayed invisible. When the second disk began throwing read errors the share went read-only and the practice called us — on the same morning their IT contractor was due to replace the failed disk and let it rebuild.
Both members were the same model from the same batch, installed on the same day, and had handled an identical write workload ever since. That is the ordinary condition of a mirror and it is exactly why they wear together. The first disk carried several hundred reallocated sectors and a growing pending count; the second, still nominally healthy, had begun accumulating its own. Crucially, the bad regions were not in the same places.
The rebuild was stopped before it started. A rebuild reads the surviving member end to end and writes across the replacement — on a survivor already carrying unreadable sectors, that is the operation most likely to fail partway and leave nothing usable. Instead both disks were imaged read-only with retries limited and unreadable sectors logged rather than allowed to stall the clone.
The two images were then merged sector by sector: wherever one disk had failed to read, the other supplied it. Because their bad regions did not overlap, the composite was complete even though neither individual image was. The file system was rebuilt from that merged image.
The volume mounted cleanly from the composite. Client ledgers were opened in their accounting software rather than merely listed, the folder structure was checked against the practice’s own expectations, and the whole set returned on fresh media.
A complete recovery, from two disks neither of which could have produced it alone. The practice replaced both members rather than one, which is the correct response to a mirror whose halves have aged together — replacing only the failed disk leaves you rebuilding onto a survivor that is next in line.
Rebuilding a mirror is normally safe when the surviving member is genuinely healthy. It is not when both are degraded: the rebuild reads the survivor from end to end, and a failure partway leaves you with two damaged disks instead of one usable image. If either member shows reallocated sectors, image both before rebuilding. RAID, NAS and server recovery starts from £500 +VAT after a free 48-hour diagnostic.
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Usually, and often completely. Each member is imaged read-only and the images merged — wherever one disk could not read a sector, the other normally can. Because the two rarely fail in the same places, the composite is frequently complete even though neither disk is.
Because they are almost always the same model from the same batch, installed together and given an identical write workload ever since. Mirrors wear in parallel, which is why a degraded mirror should be treated as two ageing disks rather than one failure.
Only if the surviving member is genuinely healthy. A rebuild reads it end to end, and on a disk with bad sectors that is exactly when it fails. If either shows reallocated sectors or SMART warnings, image both first.
RAID, NAS and server recovery starts from £500 plus VAT, quoted in writing after a free 48-hour diagnostic. Physical drive-level work carries a 50% deposit with the balance due only on success.
Start with an instant online quote, or call and talk it through with us first. You'll have a clear, fixed price before any work begins.