LG NAS RAID 1 recovery: both drives on weak heads, and one head swap
Two 500GB Western Digital drives came in from an LG NAS set up as RAID 1, on the emergency service. The customer couldn't access any data, and neither drive made a mechanical noise. Both drives had bad sectors and read very slowly once copying started, because both had weak heads: the top head on one drive and the bottom head on the other. A working head from the first drive was swapped into the second, which then read at MB/s instead of KB/s, and the data was copied off it.
| Service | RAID 1 data recovery |
|---|---|
| Drive | 2 × 500GB hard drives, RAID 1 |
| Make and model | Western Digital drives; LG NAS |
| System | LG NAS |
| Symptom | No access to any data; no mechanical noise |
| Diagnosis | Bad sectors and weak heads on both drives (top head on disk 1, bottom head on disk 2) |
| Work done | Sector-by-sector copying, head swap from disk 1 into disk 2, copy of disk 2 |
| Outcome | Disk 2 copied after the head swap; data copied to a drive for the customer |
The NAS and what the customer noticed
Two 500GB WD drives from a NAS box, part of a RAID 1 configuration; the article's title names the NAS as LG. The customer couldn't access any data. There was about 30–35GB of data on the array, and neither drive was clicking, ticking or beeping.
What examination established
- On first assessment both drives seemed OK, apart from some accumulated bad sectors.
- Once copying started, both drives were reading very slowly. That pointed to weak heads on both drives.
- The weak heads were different: the top head on disk 1, the bottom head on disk 2.
What changed the approach
Because the two drives had different weak heads, the working head from disk 1 could replace the damaged head on disk 2. Disk 2 held about 5GB more data than disk 1, so the work concentrated on disk 2.
What the lab did
- Assessed both drives and found the bad sectors.
- Started copying both drives sector by sector and found both reading very slowly.
- Swapped the working head from disk 1 into disk 2. Disk 2 then read at MB/s instead of KB/s.
- Copied disk 2, then copied the data to a drive for the customer.
Engineer's notes
The good news was that even though both drives were reading slowly, it was the top head that was weak on disk 1, and the bottom head that was weak on disk 2. This meant that we could essentially swap the working head from disk 1 with the damaged head from disk 2.
Outcome for this case
Disk 2 was copied after the head swap, and its data was copied to a drive for the customer.
What this case shows
A RAID 1 keeps a full copy on each drive, but both drives can wear at the same time. Here neither drive read well on its own, and a working part from one made the other readable. Weak heads don't always click: here they showed up as very slow reading during copying.
What it doesn't show
How long the work took, or what it cost.
Related: RAID 1 data recovery · NAS data recovery
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