A desktop enclosure holding two drives configured as a mirror — redundancy against exactly this sort of thing. What failed was the one component the mirror could not protect against: the enclosure that knew how to read it.
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A video production company used a My Book Duo in mirrored mode as its archive of delivered work, chosen specifically because two copies felt safer than one. After a power event the unit powered on, made no unusual noise, and was not detected by any machine.
Roughly six years of delivered projects were on it. The company had assumed that with two mirrored disks, a failure of one would be survivable — which is true, and was not what happened.
no bad sectors, no mechanical symptoms, full capacity on each — the mirror had done its job perfectly.
which is the single point of failure a mirror inside one box cannot protect against, since the RAID and the encryption both live in the enclosure.
the array metadata and the encryption were handled by the controller, so an individual drive presented as unformatted.
This is the limitation of enclosure-based RAID. Redundancy protects against a disk failing; it does nothing about the controller, the power supply or the bridge, all of which are shared and none of which are duplicated.
Both disks were imaged read-only, and the enclosure’s controller board retained — as with any WD unit, the encryption key material lives there rather than on the disks, so the original board was needed to make the images readable.
With the key recovered, the images were decrypted and the mirror layout derived from them: on a two-disk mirror the members should be identical, so verifying that and selecting the cleaner of the two was straightforward. The NTFS volume mounted from the resulting image without repair.
Everything. Both disks were healthy and the mirror was intact — the only obstacle had ever been the enclosure standing between the data and anything able to read it.
Delivered project files were opened and video played end to end rather than counted, and the archive was returned on a fresh external drive.
A mirror inside a single enclosure protects against one thing: a disk failing. It does not protect against the controller, the power supply or the bridge, and on WD units it does not help at all if the board holding the encryption key is lost — which is why these must be sent complete rather than as bare disks.
If two copies matter, they should be in two places rather than two bays. Multi-bay enclosures are priced as array work, from £500 +VAT after a free 48-hour diagnostic.
Drop the drive at our Oxford Science Park reception, or post it to us — it costs nothing to find out what happened. You get a written figure from the fixed bands before any work begins.