A solid state drive (SSD) has a finite number of write cycles it can perform before wear begins to degrade performance and eventually causes the drive to fail. This is an important consideration when choosing an SSD, as the write endurance will determine the usable lifespan of the drive.
What determines SSD endurance?
There are a few key factors that affect SSD endurance:
- NAND flash technology – SLC, MLC, TLC, QLC. Higher density chips tend to have lower endurance.
- Over-provisioning – Extra unused NAND capacity to replace worn out cells.
- Wear-leveling algorithms – Distributes writes evenly across all cells to prevent early failures.
- DRAM cache size – Larger cache buffers more writes before committing to NAND.
- Drive capacity – Higher capacity drives spread writes over more cells.
In general, consumer-grade SSDs with TLC or QLC NAND have lower endurance ratings around 300-1000 writes per cell. Enterprise and prosumer SSDs with MLC or SLC NAND often have endurance figures in the 3000-10000+ range.
Endurance Ratings
SSD endurance is commonly measured in two metrics:
- TBW (TeraBytes Written) – The total amount of data that can be written to an SSD before it is likely to fail. This is calculated from the P/E cycles and drive capacity.
- P/E Cycles – Program/Erase cycles. The number of times each NAND cell can be rewritten before wearing out.
As a general guideline:
- MLC NAND – 3000 to 5000 P/E cycles
- TLC NAND – 1000 to 3000 P/E cycles
- QLC NAND – 300 to 1000 P/E cycles
However, endurance can vary significantly between SSD models and manufacturers. The controller and NAND process can greatly affect the total TBW rating.
1TB SSD Endurance Example
Let’s look at an example 1TB TLC NAND SSD rated for 600 P/E cycles with 150TBW endurance:
- NAND P/E cycle rating: 600
- Drive capacity: 1000GB or 1,000,000MB
- Rated TBW endurance: 150TBW
To estimate writes:
- Divide drive capacity by PE cycle rating to get writes per cell:
1,000,000MB / 600 writes per cell = 1666 writes per cell - Multiply writes per cell by drive capacity to estimate total writes before wearout:
1666 writes per cell x 1,000,000MB capacity = 1,666,000,000 writes
So for this example 1TB SSD, each cell can withstand about 1666 write cycles. With 1TB total capacity, the estimated lifetime writes would be 1.666 billion writes before exceeding the 600 P/E cycle per cell rating.
In the 150TBW rating, we are given the total terabytes written for the whole drive. To convert to writes:
- 150TB = 150,000GB
- 150,000GB x 1024 = 153,600,000,000 writes
The 150TBW rating converts to about 153.6 billion writes for the entire 1TB SSD. This matches closely with our estimate of 1.666 billion writes x 1000MB = 1.666 trillion writes.
So for a real world example, a typical 1TB TLC SSD with 150TBW endurance can withstand around 150 trillion write operations across the entire drive before wear makes it unusable.
Factors Affecting Lifespan
In practice, the average consumer SSD will often outlive its rated endurance for a variety of reasons:
- Most consumer workloads are read heavy. The average user device might write 20-30GB daily.
- Some sector lifespans exceed ratings by 2-3X thanks to Wear Leveling and over-provisioning.
- Not all data is rewritten frequently, increasing lifespan of static data.
- Actual SSD capacity is larger than advertised due to over-provisioning.
Heavy write workloads like video production, virtual machines, and database servers will approach closer to the endurance ratings.
Let’s look at some examples of real-world write endurance:
| Usage Scenario | Daily Writes | Lifespan |
| Light Consumer Use | 20GB | 7-8 years |
| Moderate Consumer Use | 50GB | 3-4 years |
| Heavy Consumer Use | 100GB | 1.5-2 years |
| Video Production | 200GB+ | 8-12 months |
Even for a heavy prosumer workload of 100GB daily writes, the SSD would outlive its 150TBW rating due to real-world factors. But for extremely write-intensive applications, the endurance rating remains a practical limit.
Increasing Endurance
For use cases demanding heavier write workloads, there are a few options to extend SSD lifespan:
- Purchase an Enterprise or Pro SSD with higher endurance ratings. For example Samsung PM983 15.36TBW vs. 860 EVO 0.6TBW.
- Use SLC cache modes to increase performance and reduce wear when possible. Enabled on some SSDs like Intel DC P3600.
- RAID SSDs for performance and distribute writes across drives. A RAID 10 of four SSDs can quadruple endurance.
- Reduce unnecessary writes from the OS and applications. Enable TRIM, limit caches and temporary files.
In server environments demanding high performance and endurance, Intel Optane SSDs deliver exceptionally high write endurance up into the petabyte range thanks to innovative 3D XPoint memory.
Monitoring Wear Level
To check the current wear state of an SSD, tools such as SSDLife and CrystalDiskInfo can read the wear out indicator from S.M.A.R.T data. This percentage indicates what portion of the drive’s rated lifespan has been used.
SSD firmware will also attempt to prevent catastrophic failures from worn-out cells by throttling performance and remapping bad blocks. Once a drive reaches its total TBW rating, it is considered worn out but may continue functioning in a read-only or reduced capacity mode.
Conclusion
While SSD endurance continues to improve with new technologies like 3D NAND, it remains a limiting factor compared to traditional hard drives. However, consumer SSDs today generally provide adequate lifespan for most users thanks to the combination of high P/E cycle ratings and workload optimizations by the SSD controller and host system.
For write-intensive applications, choosing an enterprise-class SSD with higher endurance ratings and features will help maximize lifespan and performance. And regardless of workload, monitoring wear levels and optimizing unnecessary writes will help ensure an SSD lasts for years of service.