RAID Array in Degraded Mode: Urgent Steps to Save Data
Do you see "DEGRADED" status on your RAID controller? Management interface glowing orange or red? You have hours, maybe just minutes, before the situation can dramatically worsen.
Degraded state means one disk has failed and RAID is running on redundancy. Array still works, but another failure means data loss.
What Degraded Status Means
Definition
RAID array is in degraded state when one or more disks have failed, but the number of failures hasn't exceeded the RAID configuration's tolerance:
| RAID type | Tolerates failure | Degraded at |
|---|---|---|
| RAID 1 | 1 disk | 1 failure |
| RAID 5 | 1 disk | 1 failure |
| RAID 6 | 2 disks | 1-2 failures |
| RAID 10 | 1 per mirror | 1 failure in pair |
How Array Continues to Work
When reading data from failed disk area, RAID calculates missing data from parity (RAID 5/6) or reads from mirror (RAID 1/10). This works, but:
- It's slower
- Stresses remaining disks
- Another failure = catastrophe
Why It's a Critical State
No reserve: With RAID 5 in degraded state, a single bad sector on remaining disks means data loss.
Increased load: Remaining disks compensate for failure. More work = higher risk of another failure.
Domino effect: Disks from same batch have similar age. If one failed, others are probably close.
How Quickly to Act
Risk Timeline
First hours: Array works, but every minute of operation increases risk. Remaining disks are under stress.
Days: Risk of another failure grows exponentially. Statistically, many disks have similar lifespan – if one went, another may follow soon.
Weeks/Months: Company ignores warnings. "It works after all." Until the moment it stops working.
Rule of Thumb
The older the disks, the faster you must act. Array with new disks has more time. Array with 5-year-old disks is a ticking time bomb.
NEVER Do These Things
1. Don't Replace Multiple Disks at Once
Why people do it: "One disk already failed, I'll replace all old ones while I'm at it."
What happens:
- You remove multiple disks
- Controller loses information
- Array may be initialized (= deleted)
- Loss of all data
Correct: Replace only one failed disk. Wait for rebuild completion. Only then possibly another.
2. Don't Force Rebuild
What is "Force Rebuild": Command that forces controller to start rebuild despite warnings.
When it destroys data:
- When controller doesn't know which disk is current
- When metadata is corrupted
- When failed disk is incorrectly identified
Correct: Without certainty what you're doing, better don't force rebuild. Contact expert.
3. Don't Initialize Array
Difference Initialize vs Rebuild:
- Rebuild: Restores data from parity to new disk
- Initialize: Creates empty array, deletes everything
Why it happens: Buttons are close together in interface. One click decides about data.
Correct: Triple-check before any click. If unsure, don't click.
4. Don't Disconnect Additional Disks
Why people do it: "I'll try pulling out and returning disk, maybe it helps."
What happens:
- Controller loses sync
- Disk confusion may occur
- Metadata may be corrupted
Correct: Leave disks in place. Document state. Call for help.
5. Don't Install Recovery Software on Array
Why it doesn't work: Recovery software is designed for individual disks, not RAID arrays. It has no way to interpret striping and parity.
What it can worsen: Software may cause additional writes to array, which can overwrite data.
Correct: Recovery software only on sector copies of disks, never on live array.
What TO DO Correctly
Step 1: Stop Operations
- Inform users about outage
- Shut down applications using RAID
- Minimize I/O on array
- Don't power off server (yet – metadata in RAM would be lost)
Step 2: Document
Photograph:
- LED status on disks
- Management interface
- Event logs
Write down:
- What happened before failure
- Exact time
- Any error messages
This is critical for diagnostics and potential recovery.
Step 3: Backup What You Can
If array is still readable:
- Prioritize most important data
- Copy to external storage
- Don't copy everything at once (too much load)
Caution: Copying stresses remaining disks. Balance risk of another failure vs. value of backup.
Step 4: Contact Expert
What to say when calling:
- RAID type (0, 1, 5, 6, 10)
- Number and capacity of disks
- Controller model
- What happened and when
- Data criticality
What to prepare:
- Server access (physical or remote)
- Contact for IT person
- Decision-making authority (who approves expenses)
Can I Operate Degraded RAID?
Short-term (hours): Possible
If you must complete critical process, degraded RAID can run. But:
- Minimize load
- Monitor state
- Be prepared for failure
Long-term: NO
Risks of continuation:
Another disk failure: One bad sector on remaining disks = data loss
Overheating: Remaining disks work more, generate more heat
Power failure: In degraded state, array is more vulnerable
Psychological trap: "It works after all" – until the moment it doesn't
Details about failure causes →
Monitoring and Prevention
SMART Monitoring
Monitor SMART values of all disks:
- Reallocated Sector Count: Growing = disk dying
- Current Pending Sector: Non-zero = problem
- Spin Retry Count: Non-zero = mechanical problem
Alerting
Set up notifications for:
- Degraded status
- SMART warnings
- High disk temperature
- Unusual event logs
Hot Spare
Disk connected to array but unused. During disk failure, automatically replaces failed disk and starts rebuild.
Advantages:
- Automatic response
- Shorter degraded time
Disadvantages:
- Rebuild is still risky
- Cost of unused disk
Regular Checks
- Monthly RAID status check
- Quarterly SMART value check
- Annual review of configuration and capacity
Case Study
Situation
Medium-sized company with 8-disk RAID 5 on file server. Used for 4 years. One disk failed.
What Happened
IT technician saw "RAID Degraded" and ordered new disk. But since server "worked", no one rushed. Disk arrived in 5 days.
Day 4: Second disk failed. Data lost.
What They Should Have Done
- Immediately minimize operations
- Backup critical data to external disk
- Order disk with express delivery
- Consider professional help for safe rebuild
Lesson
- Degraded status = urgent state
- Time works against you
- 4-year-old disks are in risk zone
- Cost of express delivery is fraction of cost of lost data
FAQ
How long can RAID run in degraded state?
Technically indefinitely. Practically: The longer, the higher risk. We recommend resolving within hours, not days.
Can I replace disk myself?
If you have experience and are confident: yes. Key is:
- Correctly identify failed disk
- Use compatible replacement disk
- Don't choose "Initialize" instead of "Rebuild"
If unsure, better call us.
What if another disk fails?
For RAID 5: Data loss (no redundancy) For RAID 6: Still works, but very critical state For RAID 10: Depends which disk (different mirror pair = OK)
Need Help?
If you have RAID in degraded state and are unsure about next steps, we're here 24/7.
24/7 Hotline: +420 775 220 440