When One Stripe Group Breaks Consensus and the Entire Array Refuses to Assemble
A RAID 50 array is only as strong as the agreement between its RAID-5 groups.
When one group suddenly shows a Foreign Config, the controller is telling you:
“This stripe group no longer matches the others — and bringing it online would risk corruption.”
You may see:
- All drives physically present
- All drives showing Online / Good
- Only one group flagged as Foreign or “Inconsistent”
- And the entire RAID 50 virtual disk offline
This page explains why one group going “foreign” breaks the entire RAID 50, what caused it, and what not to do next.
What You See
- Controller UI shows:
- Foreign Config Detected on 1–3 drives
- A single RAID-5 group labeled:
- “Inconsistent”
- “Foreign”
- “Degraded / Missing Member”
- “Unknown / Offline”
- Other groups appear healthy
- The RAID 50 virtual disk is Offline, Missing, or Failed
- Drive statuses vary:
- Some drives show Foreign (Unconfigured Good)
- Others show Online but with mismatch metadata
- Logs may include:
- “Foreign Metadata Detected”
- “VD cannot be assembled — group layout mismatch”
- “Inconsistent span state”
Why It Happens
A RAID 50 relies on all RAID-5 groups producing aligned, synchronized parity stripes.
If one group presents metadata that disagrees with the others, the controller halts assembly to avoid cross-group corruption.
Common reasons:
1. Cache/NVRAM epoch drift
- A write cycle completed on Group A
- But Group B never committed because of:
- power loss
- forced shutdown
- cache battery failure
- Now their parity epochs disagree.
2. Unclean member movement
- Drives reseated during maintenance
- Moved to different slots
- Inserted into the wrong port order
- Controller sees the mismatch and flags the group as Foreign.
3. Background initialization or verify interruptions
- One group paused during parity verify
- Another group completed
- Controller now treats them as out-of-sync.
4. Latent sector errors or timeouts on a single member
- A single slow or damaged drive misreported state
- Caused the controller to mark the group “uncertain,” not failed
- Result: Foreign Config instead of Dead/Failed
5. Controller firmware or NVRAM corruption
- Corrupted group maps
- Stale “previous config” info
- Lost stripe-size or rotation metadata
Regardless of the cause, a single group in foreign state can invalidate the entire RAID 50 until corrected.
What NOT To Do
These actions destroy recoverable metadata and often make RAID 50 unrecoverable:
- Do NOT import foreign config blindly
Most imports overwrite the surviving groups’ metadata with the foreign group’s stale map. - Do NOT clear foreign config before imaging
Clearing foreign wipes the exact information needed to rebuild the correct RAID-5 group. - Do NOT force drives online regardless of state
This can combine mismatched epochs and destroy parity alignment. - Do NOT delete and recreate the RAID 50
Even with identical settings, this overwrites critical group headers. - Do NOT run filesystem repair tools
If the VD temporarily comes online, repairs will write over corrupt stripes.
Treat the foreign group as evidence — not something to “fix” until imaged.
What You CAN Do
Safe triage steps:
- Document the current controller state
- Group membership
- Flags for each drive
- Which span shows foreign state
- Export all controller configs
Including:- NVRAM dump
- Foreign config report
- Virtual disk map (if available)
- Label every drive
Slot → serial → group ID → WWN
Critical for restoring proper group order. - Clone every member drive
RAID 50 failures often hide latent errors.
Work from images, not originals. - Extract on-disk metadata
- Compare group headers
- Validate each member’s parity epoch
- Identify mismatched layout tables
- Rebuild virtually on images
- Reconstruct the RAID-5 group showing foreign state
- Validate parity
- Reassemble RAID 0 layer across groups
- Bring virtual RAID 50 online for controlled filesystem repair
This is the workflow ADR performs for any RAID 50 with a foreign stripe group.
Diagnostic Overview
- Array Type: RAID 50 — RAID-5 Groups Striped in RAID-0
- Controller State: One Group Marked Foreign; Virtual Disk Offline
- Likely Cause: Epoch Drift, Stale Metadata, Slot Mis-Order, or Interrupted Background Tasks
- Do NOT: Import Foreign Config, Clear Foreign, Force Drives Online, or Recreate the Array
- Recommended Action: Capture Metadata, Clone All Drives, Extract Group Headers, Rebuild Group Virtually, Reassemble RAID-0 Layer