Symptom:
Your RAID 10 array has dropped offline. On inspection, one full mirror pair is missing or unreadable — either due to drive failure, disconnection, or controller confusion.
What It Likely Means:
RAID 10 works by striping across multiple mirrored pairs. But if a whole pair goes missing — even if the rest of the array looks healthy — you’ve lost critical data redundancy and the stripe is now broken.
Here’s why this is dangerous:
- Even if only two drives failed, if they were in the same mirror pair, the array can’t function.
- Most RAID 10 controllers don’t distinguish between “one disk per pair” failed (survivable) vs. “both disks in one pair” failed (not survivable).
- Some controllers will continue to attempt a mount or rebuild — putting all data at risk.
What Not To Do:
- Do not force an import or try to recreate the array manually — especially if one or both missing drives just “aren’t showing up.”
- Do not reinitialize or reassign drives hoping to trigger a rebuild. This often results in irreversible overwrites.
- Don’t assume a partial volume mount means the data is safe. It may be mounting from incomplete mirror data, corrupting as you go.
✅ What You Can Do:
- Label the known-good drives immediately.
- Power off the system and image all drives if possible — especially the ones still showing.
- Check if the missing pair was mirrored together — if so, data recovery will be necessary.
When to Escalate:
If:
- You’re unsure which drives belonged to which mirror pairs
- You’ve swapped drives and still see “one pair missing”
- Your controller shows degraded or offline but all drives seem OK
It’s time to pause and escalate.
✅ Try This First:
Run JeannieLite (our non-invasive RAID diagnostic tool) to confirm:
- Which drives the controller still recognizes
- Drive health
- Mirror mapping clues
Then give us a call.