Dell PowerEdge RAID 5 recovery: one drive left out
A three-drive RAID 5 array from a Dell PowerEdge T110 II server was reconstructed from sector-by-sector copies of its disks. One drive had dropped off the array a long time ago, and leaving it out gave a full file tree without errors.
| Service | RAID 5 data recovery |
|---|---|
| Drive | 3 × 500GB hard drives, RAID 5 |
| Make and model | WD5003ABYX |
| System | Dell PowerEdge T110 II server |
| Diagnosis | One drive had dropped off the array a long time ago |
| Work done | Sector-by-sector copies of the disks, RAID parameters identified, array reconstructed without that drive |
| Outcome | A full file tree without errors |
The server
A Dell PowerEdge T110 II with 3 × 500GB WD5003ABYX drives configured as RAID 5.
What examination established
One drive had dropped off the array a long time ago. RAID 5 can keep running with a failed drive, so the array had carried on without it. This came out of diagnosing each disk.
What changed the approach
The drive that had dropped off was left out of the reconstruction.
What the lab did
- Took the server apart and diagnosed each disk.
- Copied the disks sector by sector to working drives, so the later steps ran on the copies and not the originals.
- Analysed the copies to identify the RAID parameters, and reconstructed the array on R3's own machines.
- Left out the drive that had dropped off the array, and rebuilt the file system structure.
Engineer's notes
In this case, we had to exclude one of the drives from the reconstruction process as it had dropped off the raid a long time ago (RAID 5 can still operate with a failed drive, remember?) By only removing one of the devices, we were able to obtain a full file tree without errors; luckily there were three drives only, so the process was not too complicated.
Outcome for this case
A full file tree without errors.
What this case shows
Because RAID 5 keeps working with one drive missing, this drive had dropped out long before the array came in. A degraded array can still serve data. Here the reconstruction worked once that drive was left out.
What it doesn't show
How long the array ran without that drive. That leaving a drive out is right for every failed array. How long the work took, or what it cost.
What this means if your RAID 5 looks like this
- A RAID 5 keeps working with one drive missing, so a failed drive doesn't always stop the array.
- A drive that dropped out early holds out-of-date data. Mixing it back in can spoil the reconstruction, which is why this one was left out.
- Don't start a rebuild. Stop and contact us first.
Related: RAID 5 data recovery · QNAP RAID 5 recovery after a power outage: a different problem, healthy drives but lost structure
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