When RAID 5 Disappears Without a Drive Failure
Everything looked normal. No red lights, no “failed” drives… yet your RAID 5 went offline, the volume vanished, or the OS suddenly reported the array as degraded or missing.
This is one of the most unsettling RAID 5 failures — not because hardware broke, but because the controller saw something it couldn’t trust.
RAID 5 only tolerates one missing symbol. If a survivor disk returns unreadable sectors, or metadata drifts out-of-sync, the controller may take the array offline before destructive writes occur. It feels like everything failed at once — but the truth is the system was protecting your data.
What You See
- Array marked Offline, Degraded, or Missing
- All drives report Online or OK
- Logs show UNC, CRC, or “fatal sector”
- Foreign config warnings even though hardware is unchanged
- Volume that worked yesterday now refuses to mount
Why It Happens
Even with no failed disks, RAID 5 can collapse when:
1. A survivor drive hits a latent sector error (LSE)
One unreadable block = an entire stripe with two missing symbols, which RAID 5 cannot reconstruct.
(Ref: TN-R5-001 §3)
2. Metadata becomes desynchronized
Reboots, stalled writes, or cache/NVRAM drift can make an otherwise healthy array fail validation.
(Ref: TN-R5-001 §6)
3. Controller mis-reads layout identity
Unexpected but common after:
- Rapid reboots
- Power events
- Drive unseat/reseat
- Cold boot with staggered spin-up
(Ref: TN-R5-001 §4)
4. “Foreign” configuration appears even though nothing changed
This usually indicates a mismatch between what the controller expected and what the drives presented.
(Ref: TN-R5-001 §4, §8)
What NOT To Do
- Do NOT import foreign configuration blindly
- Do NOT attempt a rebuild
- Do NOT run filesystem repair (chkdsk, fsck)
- Do NOT initialize or format the volume
- Do NOT try random drive order swaps
Each of these risks overwriting the only remaining consistency evidence.
What You CAN Do
- Power down cleanly
- Clone all members sector-by-sector
- Capture controller config and NVRAM/cache state
- Verify per-disk SMART, pending, and reallocated sectors
- Analyze parity consistency on images
- Reconstruct a safe virtual RAID using recovered layout parameters
If the array hosts production data, stop here and call ADR — further DIY attempts can hide the original parity map beyond recovery.
Diagnostic Overview
- Array Type: RAID 5 — Single Parity Set
- Controller State: Online Members / Array Offline or Foreign
- Likely Cause: Latent Sector Error or Metadata Epoch Drift
- Do NOT: Import Foreign Config or Attempt Rebuild Before Imaging
- Recommended Action: Clone All Members, Validate Parity, Follow ADR Triage Flow
RAID Triage Center – RAID 5 Triage – RAID 5 Technical Notes