By manufacturer
Dell PowerEdge HPE ProLiant Lenovo ThinkSystem Fujitsu Primergy Supermicro IBM System x / Power Acer AltosRAID 5: distributed parity. Recovery after a second disk failure is almost always possible.
RAID 5 survives the loss of one disk; when a second one fails the array is marked failed, but the data is almost always recoverable. We work on clones of the surviving disks, rebuild the parity logically and recover the filesystem. This is the scenario we see most often in our recovery cases.
RAID 5, second disk down, rebuild failed.
The canonical sequence in our cases: a RAID 5 array with one disk already degraded (an unhandled predictive failure), a second disk that fails, and the automatic rebuild attempted by the system fails because the first disk was in fact already at its limit. The array is marked crashed and the volume will not mount.
What NOT to do at this point: do not reboot repeatedly, do not attempt further rebuilds, do not write to the disks. Power down, document, call us. In depth: the second-disk failure scenario.
Cloning, analysis, logical reconstruction.
- Bit-by-bit cloning of every disk (including the failed ones, where possible via PC-3000 / DDR).
- Slot order identification: from the controller metadata (DDF / proprietary) or by analysing the data/parity pattern on the clones.
- Parameter calculation: chunk size, offset, parity algorithm (left/right symmetric/asymmetric).
- Logical reconstruction of the virtual array on the clones: no writes to the original disks.
- Filesystem recovery: extraction of the filesystem from the virtual array, with structural repair where needed.
The questions we get most often.
How likely is it to get the data back after a second disk fails in RAID 5?
Very likely where the disks are still physically readable, even with difficulty. Lower if the physical damage on one of the disks is severe (seized heads, dead motor). The preliminary diagnosis gives a realistic case-by-case estimate, after an initial inspection of the media.
How long does a typical RAID 5 recovery take?
From a few days to 1-2 weeks. The variables: disk size (full-disk cloning can take 24-48h per disk), the extent of physical damage (whether cleanroom work is required), and the complexity of the remaining filesystem. A detailed estimate follows the initial inspection.
How do you guarantee that you never write to the original disks?
Lab policy: the original disks we receive are hardware write-blocked for every operation. Cloning produces a full image, and that is what we work on. The original disks are returned to the customer in a documented sealed envelope.