Data Recovery Case File · NAS & Network Storage · One Member, One Mount
A Set Reporting a Missing Member That Mounts Anyway Was Assembled From What Remained
This enquiry describes a set in a state it should not be usable in. An older two-drive enclosure where the array shows "one online, the other missing or damaged", connected to a current machine, which "did mount once but then seems to have got corrupted." That single successful mount is the most informative thing here: it establishes what kind of set this is, and it also explains why the second attempt went differently.
| Media | Two-drive external enclosure with one member reported online and the other missing or damaged — volume mounting on one occasion and not subsequently |
| Reported situation | Older two-drive external enclosure in use · array reporting one member online · second member reported missing or damaged · unit connected to a current machine · volume mounting successfully on one occasion · volume not mounting subsequently · content reported as corrupted |
| Fault class | Array operating in a degraded state with one member absent — successful mount indicating a mirrored rather than striped set; degraded operation risking metadata divergence |
| Equipment used | The single successful mount treated as establishing the array type · unit powered down before further degraded operation · both members imaged individually write-blocked before any interpretation · array metadata compared between members to establish currency · volume assembled offline from the images |
The decode: what the mount proves, and why the second attempt failed
Why a set with a missing member does not usually mount at all: it depends on the type. A striped set spreads every file across both drives, so losing one loses part of everything and the volume cannot be assembled.
What his successful mount therefore establishes: this is not that. A set that assembled and presented a volume with one member absent must hold complete content on the remaining one.
Why that is the single most valuable finding: it means everything is on one drive. A mirrored set survives losing a member by design, and the survivor holds a full copy.
Why the mount nonetheless did not repeat: degraded operation is unstable. A controller running with a member it considers missing may reassess on each start and reach a different conclusion.
What the report of corruption most likely describes: the volume, not the content. An array mounted degraded and then interrupted can leave filesystem structures inconsistent while the underlying content stands.
Why the missing member is worth assessing rather than written off: missing is a status. A member reported missing may be failed, may have dropped out on a connection fault, or may simply have metadata the controller could not reconcile.
Why that distinction matters: two copies are better than one. Where the second member reads, it provides an independent version to compare against.
Why comparing them is necessary rather than optional: they may differ. A member that dropped out earlier stopped receiving updates, so the two hold different versions and which is current must be established.
What must not happen now: no further mounting and no rebuild. Each degraded start is another opportunity for the controller to write metadata, and a rebuild would overwrite the survivor onto the other member.
Why the age of the enclosure is relevant: its arrangement is proprietary. The set is assembled offline from images rather than by finding another unit of the same kind.
On the bench
The single successful mount was treated as establishing the array type — a striped set spreading every file across both members and therefore unable to assemble with one absent, so a volume that presented with a member missing must hold complete content on the remaining drive. Degraded operation is unstable, a controller reassessing on each start, which explains non-repetition and inconsistent structures. Both members were imaged and compared for currency.
The outcome
The successful mount read as establishing the array type, the unit powered down, and the volume assembled offline from individual images. Free assessment, one fixed written figure including VAT, charged per drive, with 50% of parts and labour upfront where a drive has to be opened. The decode: that one mount is your best news. A set that assembled with a member missing must hold everything on the one that remained — and the reason it did not repeat is that degraded operation is decided afresh each time.
An array that mounted once with a member missing
Power it down rather than trying again, and don't let anything rebuild — each degraded start is another chance for the controller to write metadata, and a rebuild would copy over the member you may still need. Read the successful mount as good news: a set that spreads files across both drives couldn't have assembled with one absent, so yours must hold complete content on the remaining member. The reported corruption most likely describes the volume structures rather than your files.
Power it down — call Cambridge Data Recovery on 01223 655015; that mount read as establishing the array type, both members imaged individually, volume assembled offline from the images.
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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.