Solid state drives (SSDs) have become a popular storage medium for computers due to their faster speeds and smaller form factors compared to traditional hard disk drives (HDDs). However, one question that often comes up with SSDs is how long does the stored data last before it becomes corrupted or lost? This article will examine the lifespan and longevity of data written on SSDs.
How Do SSDs Work?
Unlike HDDs that store data on spinning magnetic platters, SSDs store data in flash memory cells. These cells are arranged in blocks that can be erased and rewritten with new data. The SSD has a controller that manages where data is stored, provides wear leveling to distribute writes evenly, and retrieves data from the flash memory.
When new data is written to an SSD block, the old data in that block must be erased first. SSDs use a process called program/erase (P/E) cycles to do this writing and erasing. Each flash memory cell has a limited number of P/E cycles it can undergo before it can no longer reliably store data, typically around 3000-5000 cycles for MLC NAND flash.
What Factors Determine SSD Lifespan?
The total lifespan of an SSD depends on a few key factors:
- P/E cycle endurance – The number of P/E cycles each memory cell can endure before wear out.
- Over-provisioning – Extra flash capacity set aside to replace worn out cells.
- Wear leveling algorithms – Controls how evenly writes are distributed to avoid wearing out one cell prematurely.
- Workload – Read/write cycles and types of operations performed on the SSD.
- Flash memory type – SLC, MLC, TLC differ in P/E cycle endurance.
In general, SSD lifespan is determined more by the number of writes than the actual age of the drive. Let’s examine how each factor contributes to the lifespan of an SSD’s written data.
P/E Cycle Endurance
All NAND flash memory cells have a limited number of P/E cycles they can perform before wear out. Higher density drives such as TLC NAND have lower cycle endurance around 500-1000 cycles. MLC NAND has moderate endurance of 3000-5000 cycles. SLC NAND offers the highest endurance at typically 10,000 cycles or more.
The P/E cycle endurance rating for a flash cell is the minimum number of program-erase cycles guaranteed by the manufacturer under worst case conditions. The actual lifetime P/E cycles can be significantly higher than the rating. However, the P/E cycle endurance forms the baseline for the SSD’s total lifetime writes before complete wear out.
Over-Provisioning
SSD controllers set aside extra spare flash capacity called over-provisioning that is hidden from the host operating system. This over-provisioning space allows the SSD to replace worn out cells, perform garbage collection, and maintain performance as cells reach their endurance limits.
Most SSDs have between 7% to 28% over-provisioning. More over-provisioning means more spare area to substitute worn out cells and better write performance over the SSD’s lifespan. High-end enterprise SSDs typically have very large over-provisioning in the 20-30% range.
Wear Leveling
Wear leveling refers to the algorithms the SSD controller uses to distribute writes across all the flash cells evenly. This prevents any one cell or block from being programmed and erased repeatedly compared to the rest of the SSD. If wear leveling did not occur, repeated writes to one logical block would wear out that physical block prematurely.
The SSD controller maintains internal mapping tables to translate logical block addresses from the host to physical block locations on the flash memory. Wear leveling occurs in the background to remap logical blocks to different physical locations when needed to level wear.
Advanced wear leveling maximizes SSD lifespan by evenly spreading out writes so each flash cell wears out at approximately the same rate. Effective wear leveling is critical for optimizing the lifespan of data writes on an SSD.
Workload
The read and write operations performed on an SSD, referred to as the workload, directly impact the wear rate and lifespan of the drive. Workloads with very high sustained write throughput will cause more wear than light workloads dominated by random reads.
High capacity TLC-based SSDs often have workload limits in place to throttle performance if the drive exceeds its endurance capabilities. Enterprise SSDs designed for heavy workloads have higher performance and endurance expectations than consumer models.
The types of operations in the workload are also important. Small random writes are more straining on an SSD than sequential writes or reads. SSD controllers can optimize sequential writes more efficiently than small random writes that have high amounts of overhead.
NAND Flash Type
The type of NAND flash memory used in an SSD affects lifespan due to differences in endurance capabilities.
- SLC – Highest endurance at 10,000-100,000 cycles typically. Highest cost.
- MLC – Moderate endurance at 3,000-10,000 cycles typically. Moderate cost.
- TLC – Lowest endurance at 500-1,000 cycles typically. Lowest cost.
While TLC SSDs have the shortest lifespan, advances in controller technology employ techniques like aggressive data compression and advanced ECC to compensate for TLC’s lower endurance. Lower cost TLC NAND has enabled affordable SSDs that still offer reasonable lifespan by minimizing the impact of TLC’s lower cycle endurance.
Estimated Lifespan Examples
Now that we’ve covered the factors that influence SSD lifespan, let’s examine some examples of estimated total data written over the lifespan of real-world SSDs.
Samsung 860 EVO SATA SSD – 150 TBW
The popular Samsung 860 EVO 2TB 2.5″ SATA SSD is rated for 150 terabytes written (TBW) over its lifespan. This means the drive can endure writing 150 TB of data before completely wearing out. How long will this take for typical consumer usage?
Let’s assume the average household writes 20 GB of data daily between application installs, downloading media, editing documents, etc. At this rate, the 860 EVO could endure:
150 TB / 20 GB per day = 7,500 days of writes
That’s over 20 years at typical consumer daily writes! And that’s before any spare area from over-provisioning comes into play. This shows how consumer-grade SSDs like the 860 EVO offer more than enough endurance for many years of use.
Samsung PM9A1 Enterprise SSD – 10 DWPD
The Samsung PM9A1 is a high-end U.2 NVMe enterprise SSD designed for heavy 24/7 workloads. It’s rated for 10 drive writes per day (DWPD) over a 5-year warranty period.
DWPD represents the maximum number of full capacity writes that can be sustained per day while still meeting the warranty period. At 10 DWPD, the 1.6 TB PM9A1 can endure:
10 DWPD x 365 days x 5 years = 18,250 TBW
This extremely high endurance enables the PM9A1 to withstand over 18 petabytes of writes over its 5-year lifespan in even the most write-intensive enterprise environments.
Factors That Do NOT Impact SSD Lifespan
Some common misconceptions about what causes SSDs to wear out faster include:
- Time – SSDs do not wear out due to old age or the passage of time. Only erase/write cycles decrease lifespan.
- Reads – Reads have no impact on flash memory wear as no erase or write occurs.
- File deletions – Deleting files or formatting the drive does not reduce lifespan. The flash cells must be re-written before wear occurs.
- File types – Specific types of files or data do not affect wear. All writes consume P/E cycles equally.
In summary, any operation that does not cause an erase and re-write of the NAND flash cells will have no impact on the longevity of data. Only program/erase cycles contribute to lifespan reduction on SSDs.
Improving SSD Lifespan
There are ways to maximize the lifespan of an SSD if longevity is critical:
- Purchase an enterprise SSD designed for high endurance workloads.
- Choose SSDs with higher TBW ratings indicating better endurance.
- Enable the TRIM command in your OS to optimize garbage collection.
- Minimize unnecessary writes like temporary files or caches.
- Avoid completely filling up the SSD. Leave 10-20% free space.
- Use SLC caching technology to accelerate writes without wearing out TLC flash.
SSD lifespans today are generally long enough that average consumer workloads will exceed the useful life of the computer. But in write-intensive environments, it helps to understand best practices for maximizing SSD longevity.
Conclusions
The key points to understand about the lifespan of data written on SSDs include:
- P/E cycle endurance of NAND flash cells forms the baseline for total writes before wear out.
- Better wear leveling maximizes lifespan by distributing writes evenly across all cells.
- Higher workloads and small random writes will consume more P/E cycles than light usage.
- SLC has the highest endurance while TLC has the lowest, but is compensated by advanced controller technologies.
- Consumer SSDs can typically endure years of average workloads before nearing end of life.
- High-end enterprise SSDs endure extremely heavy writes, rated in petabytes.
- SSD lifetime is only affected by erases and re-writes, not reads or other operations.
Understanding what determines the lifespan of data written on SSDs can help predict when a drive may need to be replaced and how to maximize the longevity of the stored data.