Solid state drives (SSDs) have become increasingly popular in computers over the past decade thanks to their faster speeds, smaller sizes, and lack of moving parts compared to traditional hard disk drives (HDDs). However, SSDs are not immune to potential failures. Understanding the most prevalent modes of SSD failure can help users be proactive about prevention and data backups.
Most Common SSD Failure Modes
The three most common causes of SSD failure are:
- Write/Erase Endurance – SSDs have a limited number of write/erase cycles before the drive wears out. Consumer SSDs are typically rated for anywhere from a few hundred to a few thousand write/erase cycles. Once this limit is reached, sectors of the SSD will begin to fail.
- Controller Failure – The controller chip coordinates all read/write operations on the SSD. If it fails, the drive will become inaccessible. Some causes of controller failure include electrical issues, firmware bugs, and overheating.
- NAND Failure – The NAND flash memory chips store all the data on the SSD. Over time, some cells within the NAND can fail and become unusable. Errors begin accumulating until the drive fails.
Let’s explore each of these failure modes and causes in more detail.
All SSDs have a limited number of program/erase (P/E) cycles that their NAND flash memory cells can sustain before beginning to fail. Each cell gradually accumulates electron trap damage with each P/E cycle. The number of P/E cycles varies based on the type of NAND flash used:
- SLC (single-level cell) NAND – typically 100,000 P/E cycles
- MLC (multi-level cell) NAND – typically 3,000-5,000 P/E cycles
- TLC (triple-level cell) NAND – typically 1,000-3,000 P/E cycles
- QLC (quad-level cell) NAND – typically 300-1,000 P/E cycles
Consumer and budget SSDs often use the lower endurance TLC or QLC NAND in order to offer larger capacities at lower costs. However, this comes at the expense of shorter lifespans under heavy usage. On the other hand, higher-end SSDs aimed at intensive enterprise/professional workloads will use more durable SLC or MLC NAND rated for much higher endurance.
The P/E cycle endurance rating is derived through drive-level testing and reflects the point at which data retention errors rise above acceptable thresholds under ideal conditions. Real-world endurance can vary substantially based on usage patterns. Heavy write-intensive workloads, such as continuous writing of large video files, will cause the drive to reach its endurance limit much faster.
Most SSDs use wear leveling techniques to spread writes across all available cells, maximizing the usable lifespan. However, once a certain number of cells have reached their endurance limit, errors will escalate rapidly.
Preventing Endurance-Related Failures
Since endurance failures are predictable based on total data written, there are steps users can take to extend the SSD lifespan:
- Purchase an SSD with generous endurance ratings – Look for terabytes written (TBW) ratings rather than just P/E cycles. A higher TBW indicates it can sustain heavy write loads longer.
- Manage swap files and caches to limit writes – Configure the OS and apps to minimize unnecessary writes where possible.
- Avoid fully filling up the SSD – Wear leveling is less effective with little free space left. Leave 10-20% unused space.
- Upgrade to larger SSDs – The same workload will wear out a smaller SSD faster. Get the largest capacity suitable for your needs.
- Use SLC caching – Some SSDs reserve a portion of SLC NAND to absorb a percentage of writes and reduce wear on the main TLC/QLC storage.
The controller is the brains of the SSD, managing all read and write operations as well as error correction, encryption/decryption, wear leveling, and other key functions. Controller failures can occur for several reasons:
- Electrical – Power surges, spikes, ESD damage, or voltage mismatches can damage the controller.
- Overheating – Insufficient cooling and heavy usage leads to thermal stresses.
- Component defects – Faulty capacitors, ICs, or other parts cause the controller to malfunction.
- Firmware bugs – Code errors may trigger controller crashes.
Controller failures are less predictable than write endurance failures. Electrical damage or overheating can happen to any drive. Component defects and firmware bugs also occur randomly, requiring newer revision controllers to correct.
A failed controller will make the SSD inaccessible, as the data on the NAND flash cannot be read or written. In most cases, a controller failure means the SSD is permanently damaged. Data recovery services can sometimes extract the raw NAND data, but this is expensive with no guarantees.
Preventing Controller Failure
Some steps users can take to protect against controller failure include:
- Use surge protectors – They protect against electrical damage from power spikes.
- Check airflow – Ensure the SSD has sufficient active or passive cooling.
- Update firmware – Newer firmware may fix bugs and improve stability.
- Monitor SMART data – Tools can detect signs of impending failure like ECC errors.
- Choose quality components – Server/enterprise drives often have higher-grade controllers.
The NAND flash chips provide the underlying storage capacity in SSDs. While high quality NAND is designed for endurance, failures can still occur over time. Some common causes include:
- Write/Erase Cycling – As mentioned earlier, each cell has limited P/E cycle endurance before wear-out.
- Read Disturb Errors – Repeated reads of neighboring pages can cause bit errors.
- Retention Errors – Stored voltage in cells can deteriorate over time, especially at high temperatures.
- Bad Blocks – Factory defects or early breakdown of cells.
As NAND cells begin to accumulate errors, the SSD controller will take action to mitigate this using error correction code (ECC). However, once errors proliferate beyond the ECC capabilities, data will be lost.
ECC and Failure Prediction
To compensate for errors like those listed above, SSDs use ECC to both detect and recover from corrupted bits:
- Factory ECC – Applied during NAND programming to fix initial defects.
- On-the-fly ECC – Applied upon data reads to identify and fix bit flips.
- Read scrubbing – Periodically re-reads data blocks and uses ECC to detect/repair errors.
As ECC attempts increase to correct errors, this indicates deteriorating NAND. The SSD controller tracks metrics like the following to assess health status and predict potential failures:
- Raw bit error rate (RBER) – Rate of errors detected by ECC.
- ECC success rate – % of errors corrected by ECC.
- Bad blocks – # of unusable blocks excluded from use.
Monitoring ECC metrics can provide advance notice of SSDs approaching failure limits. Once ECC is overwhelmed, data loss escalates rapidly.
Preventing NAND Failure
Actions that can reduce the likelihood of NAND errors and failure include:
- Monitoring SMART data – Tools can show ECC counts and other metrics signaling possible issues.
- Maintaining good temperatures – Higher temps accelerate breakdown in NAND cells.
- Avoiding vibration/shock – Mechanical stresses damage NAND structures.
- Refreshing data – Occasionally reading all data forces ECC to correct bit flips.
Conducting SSD Reliability Testing
SSD and storage device manufacturers conduct extensive reliability and product testing during development to root out flaws and weaknesses before market release. Some common test methods include:
Highly Accelerated Life Test (HALT)
HALT rapidly ages SSDs by exposing them to extreme conditions beyond normal operating ranges:
- Temperature – Typically -40°C to 90°C.
- Vibration – Up to 60G vibrations.
- Humidity – Up to 90% RH.
- Voltage – Minimum and maximum specified voltages.
HALT reveals design weaknesses and component problems while confirming operation at temperature extremes. Units run through stringent HALT have high reliability at normal use conditions.
Highly Accelerated Stress Screen (HASS)
While HALT focuses on design margin testing, HASS detects early life product defects by stress screening units for a short time:
- Temperature – Typically 55°C to 70°C.
- Vibration – 3 to 6G.
- Voltage – Minimum and maximum specified.
- Time – 24-48 hours.
HASS identifies units prone to early failure, ensuring they are removed from production. Units passing HASS should have low failure rates during customer use.
Long Term Reliability Testing
Long-term reliability testing evaluates product lifetimes under normal operating conditions:
- Temperature – Room temperature up to 45°C.
- Voltage – Nominal supply voltage.
- Workloads – Simulated consumer workloads.
- Time – Months to years.
Statistical analysis of time-to-failure rates under these conditions helps establish warranty periods. Accelerated models also predict field life expectancy.
Stress Endurance Testing
Stress endurance testing determines lifetimes under high duty cycle workloads:
- 100% disk fills.
- Large sequential write patterns.
- Maximum queue depths.
- Extended duration – Weeks to months.
Analysis of errors, ECC rates, wear metrics, and failures helps quantify P/E cycle endurance and set endurance specifications.
Best Practices to Avoid SSD Failure
While SSD failures will eventually occur due to factors like write/erase cycles and component wear-out, customers can take measures to avoid premature, unexpected failures:
- Choose quality drives with ratings matching usage – budget drives may fall short in heavy use cases.
- Monitor SMART parameters for signs of issues developing.
- Keep updated backups of important data.
- Update SSD firmware when manufacturers provide fixes.
- Don’t encrypt the SSD as this limits repair options.
- Use surge protectors and adequate cooling.
- Don’tfill up the SSD completely.
Enterprise and specialist drives designed for intense workloads offer higher reliability, but at increased cost. For typical home and office applications, mainstream SSDs from reputable brands complemented by sound backup practices provide an optimal balance of performance, endurance, and value.
In summary, while SSDs are far more reliable than traditional hard drives, their NAND flash memory cells have finite lifespans. The most prevalent SSD failure modes are:
- Write/erase endurance wearing out cells.
- Controller malfunctions from electrical damage, overheating, bugs, etc.
- NAND failure from voltage breakdown, retention errors, etc.
Knowing the nature and causes of the most common failures allows users to take protective steps. Proactively monitoring health metrics can also provide early warning of issues before catastrophic data loss occurs. Combining quality drives, firmware updates, monitoring tools, and redundant backups provides the most comprehensive means of avoiding SSD failure.