Data Recovery Case File · Portable Drives · Stock Is the Constraint
A Head Assembly Must Come From a Drive of the Same Family, Firmware and Head Configuration
His enquiry has already been through one assessment and stalled on a supply problem rather than a technical one. A 4TB drive that clicked, was diagnosed as needing head replacement, where the previous attempt "has been unable to source a compatible donor for a head swap" — and it now "powers on but only appears as around four gigabytes and uninitialised." Both halves are informative: donor matching is genuinely narrow, and that capacity figure is a specific state rather than a fault.
| Media | 4TB portable hard drive requiring head assembly replacement — presenting a reduced capacity and unrecognised volume; donor sourcing unsuccessful at a previous assessment |
| Reported situation | Portable drive ceasing to function with audible mechanical activity · head failure identified at a prior assessment · compatible donor not sourced by that party · attempted recovery not completed · drive powering on · drive reporting a capacity of approximately four gigabytes · volume reported as unrecognised on multiple platforms · a lab with donor stock sought |
| Fault class | Head assembly failure with the drive in a restricted operating mode — reduced capacity reporting indicating firmware safe mode rather than data loss; recovery dependent on donor availability |
| Equipment used | Reduced capacity reporting interpreted as a firmware operating mode rather than as lost capacity · donor match established across family, firmware revision and head configuration before any opening · laminar flow bench inspection with head and platter surfaces assessed before any rotation · matched donor head assembly fitted · imaging under capped timeouts following successful initialisation |
The decode: why donors are narrow, and what four gigabytes actually means
Why a head assembly cannot be taken from any similar drive: the match is tighter than the model number. The donor must share the family, the firmware revision and the number and arrangement of heads, because the assembly is calibrated to work with a specific configuration.
Why capacity alone is not the criterion: the same stated capacity is built several ways. A drive of a given size may use different numbers of platters across production runs, and an assembly built for one arrangement will not serve another.
Why that makes stock the real constraint: it is a sourcing problem. The technique is well established, and whether it can be applied depends on holding, or being able to obtain, the right donor.
Why a previous attempt failing on that point says nothing about the drive: it is a statement about inventory. An assessment that stopped at donor sourcing reached no conclusion about recoverability.
Now the four gigabyte figure, which is easy to misread: the capacity has not shrunk. A drive unable to read its own configuration falls back to a restricted mode and reports a small nominal size, which is a state rather than a measurement.
Why that state arises here specifically: the reserved region needs working heads. A drive with a failed head cannot read the parameters describing itself, so it cannot report its true capacity or present a volume.
Why the volume being unrecognised follows automatically: the host is looking at the wrong size. A system offered a few gigabytes where terabytes should be finds no filesystem it can interpret.
Why that is reassuring rather than alarming: nothing about the recording is implicated. The content sits on the platters, unaffected by the drive's inability to describe itself.
What determines the outcome once a donor is available: surface condition. A failed head may have contacted the surface, and that is assessed under filtered air before any rotation.
What must not happen meanwhile: no further powering. Each attempt runs a drive with a failed head over the surface it cannot read.
On the bench
Reduced capacity reporting was interpreted as a firmware operating mode rather than as lost capacity — a drive unable to read its own configuration falling back to a restricted mode with a small nominal size, which is why no volume is recognised. Donor match was established across family, firmware revision and head configuration, since assemblies are calibrated to a specific arrangement and drives of identical stated capacity are built with differing platter counts across production runs.
The outcome
Capacity reporting read as a firmware mode, donor matched across family, firmware and configuration, and surfaces assessed under filtered air before rotation. Free assessment, one fixed written figure including VAT, 50% of parts and labour upfront with the balance only on successful recovery. The decode: four gigabytes is a state, not a measurement. A drive that cannot read its own configuration reports a nominal size — and the previous attempt stopped at inventory rather than at a conclusion about your data.
When a recovery has stalled on donor availability
Understand what stalled: an assessment that stopped at sourcing reached no conclusion about your data at all. Donor matching is narrower than the model number, requiring the same family, firmware revision and head configuration, because drives of identical stated capacity are built with different platter counts across production runs. Read the reduced capacity as a state rather than a loss — a drive that can't read its own configuration reports a small nominal size. Don't power it meanwhile.
Ask about stock — call Cambridge Data Recovery on 01223 655015; capacity reporting read as a firmware mode, donor matched across family, firmware and head configuration, surfaces assessed before rotation.
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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.