Why Is My SSD Stuck in Read-Only Mode or Showing Bad Blocks?
Detailed Answer
Discovering your SSD is stuck in read-only mode or reporting bad block errors is alarming — but it’s actually better than the alternative. When SSDs fail this way, they’re telling you “I’m dying, but I’m protecting your data.” This is a designed safety feature that gives you a chance to recover everything before complete failure.
Understanding why this happens and how to respond properly can be the difference between successful data migration and catastrophic data loss. This guide explains the causes, what you can do, and how to handle the situation.
Understanding SSD Read-Only Mode
Read-only mode (also called write-protect mode or fail-safe mode) is a protective state that SSDs enter when they detect critical problems. In this state:
- You can read all existing data
- You cannot write new data
- You cannot delete files
- The drive appears healthy otherwise
Why this exists: When SSDs detect they cannot reliably store new data, continuing to accept writes would corrupt existing data. By going read-only, the drive preserves what’s already stored while signaling that replacement is needed.
How SSDs decide to go read-only:
- Spare NAND blocks exhausted (wear leveling has no room)
- Too many uncorrectable ECC errors
- Critical firmware metadata corruption
- Controller detects write reliability below threshold
- SMART data shows critical parameter failure
Understanding Bad Blocks
NAND flash has a limited lifespan — each cell can only be written a certain number of times before it becomes unreliable. Bad blocks are cells/blocks that have failed or been marked unreliable.
Bad Blocks Are Normal (To a Point)
Every SSD ships with some bad blocks — manufacturing isn’t perfect. SSDs reserve “spare” blocks to replace bad ones. This is called overprovisioning, and it’s why your 1TB SSD might have 1,024 GB of NAND but only offers 1,000 GB.
The SSD controller constantly:
- Tests blocks for reliability
- Marks failing blocks as “bad”
- Remaps data to spare blocks
- Reports health via SMART data
Normal operation: A few bad blocks accumulating over years is expected.
Warning sign: Rapid increase in bad blocks indicates accelerating failure.
When Bad Blocks Become Critical
Problems arise when:
- Spare blocks run out (no room for remapping)
- Bad block rate exceeds controller’s management ability
- Critical areas (firmware, translation tables) develop bad blocks
- Error correction (ECC) can’t recover data from failing blocks
When these thresholds are crossed, the SSD must take protective action — often entering read-only mode.
Causes of Read-Only Mode and Bad Block Errors
1. NAND Wear (End of Life)
NAND cells wear out with each write cycle. TLC NAND typically endures 1,000-3,000 program/erase cycles; QLC handles 100-1,000 cycles.
How it happens:
- Heavy writes consume cell lifespan
- Cells begin failing at higher rates
- Spare blocks used up for remapping
- Eventually, no spare capacity remains
- SSD enters read-only to protect existing data
SMART indicators:
- Media Wearout Indicator near 0
- Percent Lifetime Used near 100%
- Reallocated Sector Count very high
- Remaining Reserved Block Count near 0
Affected drives: Heavily used drives, especially QLC models with lower endurance. The Samsung 990 Pro and Crucial T500 with TLC NAND have higher endurance than QLC budget drives.
2. Firmware Bugs
SSD firmware is complex software managing intricate NAND operations. Bugs can cause:
- Incorrect bad block marking
- Premature read-only triggering
- Failure to properly manage spare blocks
- Metadata corruption leading to failures
Notable firmware incidents:
- Samsung 980 Pro: Early firmware caused excessive wear reporting
- Crucial M500/M550: Firmware bugs caused sudden read-only
- Various drives: Specific firmware versions with known issues
Solution: Check for firmware updates. Some bugs are fixable; others require RMA.
3. Power Loss Corruption
Sudden power loss during writes can corrupt:
- Flash Translation Layer (FTL) tables
- Firmware metadata
- In-progress write operations
- Wear leveling data
How it triggers read-only:
- Power lost during critical write
- Metadata becomes inconsistent
- Controller can’t trust write reliability
- Drive enters read-only as precaution
Prevention: Use UPS for important systems; enable proper shutdown procedures.
4. Controller Issues
The SSD controller manages everything. Controller problems include:
- Partial failures affecting write capability
- Overheating damage
- Component degradation
- Power delivery issues
Symptoms:
- Read-only without excessive bad blocks
- Firmware unable to update
- Erratic behavior before read-only
- Detection issues alongside read-only
5. Manufacturing Defects
Some drives have defects that appear over time:
- Poor quality NAND with lower than expected endurance
- Controller binning issues
- Inadequate quality testing
- Early batch problems
Pattern: Affects multiple users with the same model around the same age.
Diagnosing the Problem
Before taking action, determine what’s actually wrong:
Step 1: Check SMART Data
SMART (Self-Monitoring, Analysis, and Reporting Technology) provides health information:
Tools to use:
- CrystalDiskInfo (Windows, free)
- Samsung Magician (Samsung drives)
- Crucial Storage Executive (Crucial drives)
- Western Digital Dashboard (WD drives)
- smartmontools (Linux/Mac/Windows)
Critical SMART attributes for SSDs:
| Attribute | What It Means | Warning Level |
|---|---|---|
| Reallocated Sector Count | Bad blocks replaced | Increasing rapidly |
| Remaining Reserved Block Count | Spare blocks available | Near zero |
| Media Wearout Indicator | % of life remaining | Near zero |
| Percent Lifetime Used | % of TBW consumed | Above 90-100% |
| Uncorrectable Error Count | Data errors ECC couldn’t fix | Any non-zero |
| Program Fail Count | Write failures | High or increasing |
| Erase Fail Count | Block erase failures | High or increasing |
Step 2: Identify the Error
Different error messages indicate different problems:
“Write protected” or “Read-only file system”:
- Drive intentionally in read-only mode
- Firmware has limited writes for safety
- May be recoverable by firmware tools
“Bad block” or “I/O error during write”:
- Specific blocks failing
- May still have write capability overall
- Indicates ongoing degradation
“Disk is write-protected” (Windows):
- Could be drive failure
- Could also be permissions/policy issue
- Test with different computer first
“Filesystem mounted read-only due to errors”:
- May be filesystem corruption, not drive failure
- Check SMART before assuming hardware issue
- Could require filesystem repair
Step 3: Rule Out Non-Hardware Causes
Before assuming hardware failure:
Check physical write protection:
- Some external drives have write-protect switches
- USB adapters may have malfunctioning switches
Check operating system issues:
- Group policy can prevent writes (Windows)
- Filesystem permissions could block access
- Mount options may specify read-only
Check filesystem health:
- Corrupted filesystem may mount read-only
- Running chkdsk/fsck might fix it
- But don’t do filesystem repair on a failing drive
Immediate Steps When Your SSD Goes Read-Only
If your SSD has entered read-only mode, act quickly:
Step 1: Stop Using the Drive for Normal Operations
Don’t:
- Try to write files
- Run filesystem repair tools
- Continue using it as a boot drive
- Install programs or updates
Do:
- Understand this is a data recovery situation
- Treat every read as potentially the last
- Plan your data migration immediately
Step 2: Copy Your Data Now
This is your priority — get data off the drive while you still can:
Best approach:
- Boot from a different drive (or use another computer)
- Connect the read-only SSD as secondary storage
- Copy most important files first
- Then copy remaining files
- Verify copies completed successfully
Tools for copying from failing drives:
- Regular file copy (if drive is stable)
- ddrescue (Linux) — handles read errors gracefully
- Roadkil’s Unstoppable Copier (Windows) — skips errors
- TeraCopy — shows detailed progress and errors
Important: Copy to a known-good drive with sufficient space. The Samsung 990 Pro 2TB or Crucial T500 2TB are excellent replacements.
Samsung 990 Pro 2TB
7,450 MB/s Read | 6,900 MB/s Write | PCIe 4.0 | 1,200 TBW Endurance | 5-Year Warranty
Ideal replacement for a failing SSD. Samsung’s flagship offers exceptional reliability, high endurance (1,200 TBW), and comprehensive warranty support.
Step 3: Check if Firmware Recovery Is Possible
Some read-only conditions can be reset:
Manufacturer recovery tools:
- Samsung: Magician may offer “Full Erase” that resets
- Crucial: Storage Executive can attempt recovery
- Intel: SSD Toolbox had recovery functions
- Some drives: ATA Secure Erase can restore writability
Warning: These tools may work but often indicate the drive shouldn’t be trusted anymore. Restored drives can fail again quickly.
Step 4: Consider Professional Recovery (If Needed)
If you cannot read data from the drive:
- Professional services can sometimes recover data from read-only drives
- Costs: $300-$1,000 for SSD recovery
- Success rate for read-only (vs dead) drives is high
Can the Drive Be Fixed?
The answer depends on the cause:
Firmware Bug Read-Only
Potentially fixable:
- Firmware update may resolve
- Manufacturer may have recovery procedure
- Factory reset/secure erase may restore function
Recommendation: Even if fixed, don’t trust the drive with critical data. Demote to secondary storage or replace.
NAND Wear Read-Only
Not meaningfully fixable:
- The NAND is physically worn out
- Firmware did exactly what it should
- Drive has reached end of life
Recommendation: Replace immediately. The drive did its job by going read-only.
Power Loss Corruption Read-Only
Sometimes fixable:
- Low-level format may restore function
- Secure erase clears corrupted data structures
- Factory reset rebuilds translation tables
Recommendation: Drive may work but reliability is questionable. Use for non-critical data only.
Controller/Manufacturing Defect
Usually not fixable:
- Hardware problem requires replacement
- May be covered under warranty
- Even if fixable, trust is compromised
Recommendation: RMA if under warranty; replace otherwise.
Preventing Future Read-Only Issues
Choose High-Endurance Drives
TLC drives with high TBW ratings last longer:
- Samsung 990 Pro: 1,200 TBW (2TB)
- Crucial T500: 1,200 TBW (2TB)
- WD Black SN850X: 1,200 TBW (2TB)
Avoid low-endurance QLC for write-heavy workloads.
Monitor Drive Health
Regularly check SMART data:
- Monthly for important systems
- Weekly for write-heavy workloads
- Automated alerts with tools like Hard Disk Sentinel
Warning signs to watch:
- Reallocated Sector Count increasing
- Program Fail Count increasing
- Remaining Spare Blocks decreasing
- Percent Used approaching limits
Maintain Good Power Hygiene
Reduce power-loss risks:
- Use a UPS for important systems
- Enable proper shutdown procedures
- Avoid forced shutdowns when possible
- Consider “Power Loss Protection” drives for critical data
Don’t Overfill Drives
Drives at 90%+ capacity work harder and wear faster:
- Maintain 10-20% free space
- Higher fill = more wear = shorter life
- Overprovisioning extends lifespan
Keep Backups
Ultimately, any drive can fail:
- 3-2-1 backup strategy (3 copies, 2 media types, 1 offsite)
- Regular automated backups
- Test restore procedures periodically
- Don’t store irreplaceable data on single drives
Frequently Asked Questions
Usually yes — that’s the point of read-only mode. The SSD detected it couldn’t reliably write new data, so it’s protecting existing data by preventing writes. Your data should be fully accessible for reading. However, don’t delay recovery — the drive’s condition may worsen. Copy everything to a new drive as soon as possible. This is a window of opportunity, not a permanent state.
Sometimes technically possible, but not recommended. Manufacturer tools may reset the drive, allowing writes again. However, the drive entered read-only for a reason — something is wrong. Even if “fixed,” the underlying problem (worn NAND, firmware issues, etc.) remains. A “fixed” drive may fail again suddenly. Use it only for non-critical data, if at all, and replace it as your primary drive.
Premature read-only usually indicates a defect or abnormal wear. Possible causes: firmware bug (check for updates), manufacturing defect (check for known issues with your model), extremely heavy writes (check total bytes written in SMART), or power event damage. If the drive is under warranty and hasn’t exceeded its TBW rating, contact the manufacturer for RMA. This isn’t normal wear.
Bad blocks are the symptom; read-only is the response. As SSDs age, individual blocks fail and are marked “bad,” then remapped to spare blocks. This is normal. When spare blocks run out, or bad block rate becomes critical, the drive enters read-only mode to protect data. Some bad blocks = expected. Rapid bad block accumulation or no spare blocks = approaching read-only. Read-only = critical state, replace drive.
Don’t run write-based repairs on a drive in read-only mode. Filesystem repair tools fix filesystem errors by writing corrections. On a read-only drive, these writes fail, potentially causing worse problems. First, verify it’s hardware read-only (not OS misconfiguration). If hardware is failing, copy data first, then repair on the destination drive if needed. Never run repair tools on drives with suspected hardware issues.
Only after copying all data, and with realistic expectations. Some manufacturer tools can reset drives to factory state, potentially clearing read-only mode. This erases all data. Success varies — sometimes it works, sometimes the drive fails completely. Don’t attempt this hoping to recover data; do it only to potentially salvage the drive for non-critical use after data is safely copied elsewhere.
Unpredictable — treat it as urgent. Some read-only drives remain readable for months; others fail completely within days. The drive’s condition varies based on what triggered read-only mode. NAND wear-out might be stable; controller issues might progress. Don’t assume you have time. Copy data immediately, within hours of discovering the issue, not days.
Related Articles
- Samsung 990 Pro — High-endurance replacement drive
- Crucial T500 — Value replacement option
- SSD Disappeared from BIOS — Complete SSD failure
- SSD Slow When Full — Why free space matters
- SSD vs HDD — Storage technology comparison
Summary
An SSD entering read-only mode or showing bad block errors is actually performing a valuable service — it’s protecting your data by refusing to accept writes it can’t reliably store. This gives you a window to recover data that sudden death wouldn’t provide. Act immediately: copy all data to a healthy drive while the read-only SSD still allows reads. Don’t attempt repairs until data is safe. The drive may be technically recoverable (firmware reset, secure erase), but the underlying issue means it shouldn’t be trusted for important data. Replace with a high-quality drive like the Samsung 990 Pro or Crucial T500, and implement proper backups so future drive failures don’t risk data loss.