A student’s MacBook Pro lost its coursework overnight — documents gone from Finder, yet the storage still full — and Disk Utility couldn’t fix it. A Fusion Drive splits one volume across an SSD and an HDD, and when the file system corrupts and the two fall out of sync, files go ‘invisible’ while the data sits untouched. We cloned both disks, rebuilt the combined file system, and recovered the lot.
A university student brought in a MacBook Pro after their coursework suddenly became inaccessible. Documents and project folders had disappeared from Finder despite nothing being deleted, yet the storage bar showed the space was still used — a strong clue the data was present but hidden. The Mac had also become slow and prone to freezing when accessing files, and Disk Utility reported file-system errors it couldn’t repair. With a thesis and a term of assignments at stake and Disk Utility unable to help, they wisely stopped rather than letting it keep trying, and sent the machine to us.
A Fusion Drive is Apple’s hybrid storage: a small, fast SSD and a large, slower HDD bound together in software so macOS presents them as a single volume. The system quietly keeps frequently-used data on the SSD and everything else on the HDD, moving files between them for speed. The important consequence for recovery is that neither disk holds a complete file system on its own — your data and the metadata that describes it are split across both, and only make sense when the two are correctly combined. Recover one disk in isolation and you get half a picture; the volume only comes back when both are reunited exactly as macOS had them.
That ‘files gone, space still used’ combination is the signature of file-system corruption rather than deletion. macOS uses APFS (with HFS+ on older setups), and the file system keeps an index — on APFS, a set of catalog and object-map trees — that records every file’s name, location and structure. When that index is damaged, macOS can no longer find the files, so they vanish from Finder — but the actual file data is still occupying the disk, which is why the space never freed up. On this machine two things had gone wrong together: the APFS structures were corrupt, and the SSD and HDD had fallen out of sync, so even the parts macOS could read didn’t line up. The data was all there; the map to it was broken.
Disk Utility’s First Aid checks and repairs a file system in place, on the live volume — and on a corrupt, desynchronised Fusion Drive that’s both risky and limited. It has no safe way to reunite an out-of-sync SSD and HDD or to reconstruct badly damaged APFS structures, and running it repeatedly on the live drive can make matters worse by writing changes over the very metadata a recovery needs. A “First Aid failed” on a Fusion Drive isn’t unusual; it’s the tool reaching the edge of what it can do. The safe approach is to stop, image both disks, and rebuild everything on the copies.
The two Fusion Drive components were handled individually: each of the SSD and the HDD was cloned sector by sector to healthy storage, write-blocked, using forensic imaging so the originals were never altered. Working from the images, the Fusion (logical) volume was reassembled — combining the SSD and HDD in the correct relationship so the single volume they formed reappeared — and then the APFS file system was rebuilt. APFS is a copy-on-write design that retains earlier checkpoints of its structures, and those, together with the intact metadata copies, gave consistent reference points to reconstruct the catalog and re-link the files to their data. That restored the directory tree, so the coursework came back with its real names and folders rather than as loose fragments.
With the volume rebuilt, the student’s files were extracted and checked — the thesis and research documents, lecture notes, presentations and assignments — and every file confirmed to open intact before sign-off. The full set, a complete recovery, was delivered on a fresh external SSD so studies could carry on without delay. The advice we passed on is worth repeating for anyone on a Fusion Drive or any single Mac: file-system corruption strikes without warning and hides data rather than announcing itself, so keep coursework and irreplaceable work backed up (Time Machine or a cloud copy), and if files disappear while the disk stays full, stop using the Mac and don’t keep running repairs — the data is very often still there to be rebuilt.
Individual forensic imaging of both Fusion Drive disks (SSD + HDD), write-blocked · reassembly of the combined logical volume · APFS reconstruction using checkpoints and backup metadata · HFS+ support for older setups · extraction and verification of documents. All work in-house at our Belfast lab.
That usually means file-system corruption, not deletion — the data is still there, just hidden. Stop running First Aid and send the Mac or its drive in for a free, no-obligation diagnostic. We’ll tell you what can be recovered and put a fixed price in writing before any work starts, and on most jobs it’s no fix, no fee. Post it in from anywhere in the UK, or drop it to us in Belfast.
That’s almost always file-system corruption rather than deletion. The index that tells macOS where your files are has been damaged, so the files vanish from Finder — but the data itself is still on the disk, which is why the space is still used. Rebuilding the file system usually brings the files back with their names and folders intact.
It adds a step. Because a Fusion Drive splits one volume across an SSD and an HDD, both disks have to be imaged and correctly recombined before the file system can be rebuilt — recovering just one won’t work. It’s very doable, but it’s why standard tools and DIY attempts usually can’t handle a corrupt Fusion Drive.
Usually not. First Aid only repairs a file system in place on the live disk and can’t reunite an out-of-sync Fusion Drive or rebuild badly damaged APFS structures — and running it repeatedly can make things worse. Imaging both disks and reconstructing the volume and file system on the copies, the way we do, recovers the data in the great majority of cases.