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Solid state drives (SSDs) offer faster data access due to their rich internal parallelism. They have numerous advantages, like faster boost-up speed, energy efficiency, better resistance, and compact size. They are also more durable when compared to other storage options.
However, SSDs also have their limitations. SSDs store data using flash memory electronically. The cells wear out with time and become less efficient, affecting the drive’s usable life cycle.
How Long Does an SSD Last?
SSDs use flash memory for data storage. Using NAND flash chips, similar to the ones used in flash cards or USB drives, SSDs read and write data electronically. They rely on integrated circuits for data storage and consist of a transistor grid that stores data on the binary coding system.
The SSD relies on an integrated circuit for data storage. It has an electronic controller and a series of NAND chips. These chips do not need a power supply for operation. Instead, they consist of a transistor grid that stores data on the binary coding system.
The binary coding system has two states: 0 and 1. When there is current flowing in the transistors, their state is 1. When there is no current, the value remains 0. Initially, the transistors are in the 1 state. When the file is written, or a save operation is performed, some transistors are blocked, and their value becomes 0.
Even if SSDs are much faster than mechanical hard drives, they have non-volatile memory. As a result, they become less reliable with time since the transistors wear out and lose their charge-holding capacity. With growing usage, these drives become less reliable. By default, SSDs come with a limited lifespan.
With every writing process, the SSD becomes less efficient. This is because to overwrite data, the existing data must be erased first. For this, NAND chips require voltage to send electrons through the insulator.
With continuous write and erase cycles, the insulator wears out. Therefore, the flash cells cannot be programmed and erased indefinitely. Thus, the NAND design and SSD usage determines how long it will last.
Read more about the benefits of SSDs.
What Factors Affect the SSD Lifespan?
There are mainly three factors that help determine SSD reliability: the age of the SSD, total terabytes written over time (TBW) and drive writes per day (DWPD).
The age of the SSD
The age of the SSD determines its performance and longevity. Even if manufacturers claim that they can last for ten years, the average lifespan of an SSD is less than ten years. Above all, it depends on the usage.
As per the research report of Google and the University of Toronto, drive failures increased with the age of the SSD. However, they needed to be replaced 25% less often than hard disk drives.
Total terabytes written over time
In the IT industry, the lifespan of an SSD is in TBW. Mostly the service life of an SSD is 256 TBW. This is the basic warranty period after which the memory cells start degrading.
The chances of drive failure and data loss increase after exceeding the TBW value. Therefore, replacing the drive after the assigned TBW gets used up is recommended.
Drive writes per day
SSDs also have a DWPD value that refers to the data that can be written each day within the warranty lifespan of the SSD. It is measured in gigabytes. If the DWPD value is more, the SSD shows greater endurance. So, when purchasing an SSD, you can consider the DWPD for better capacity and performance.
How SSD/Flash Endurance is Measured
The endurance rating of NAND flash SSDs is expressed in write cycles. They have a limited number of write cycles, after which the oxide layer of the flash memory cells starts degrading. This impacts the performance of the SSD.
The endurance rate is also called the program/erase cycle, or P/E cycle. When new data is stored in the SSD, an existing data block must be erased electrically. Unfortunately, a continuous P/E cycle deteriorates the oxide layer of the NAND flash memory cells. Thus, these cells eventually wear out, which affects their data-storing capacity.
Another undesirable phenomenon that affects SSD performance is write amplification. When writing data into the storage drive, the actual amount of the write gets multiplied. This increases the number of writes and thus shortens the reliable operation time of the SSD, crashing its consistency. Different factors affecting the write amplification are garbage collection, over-provisioning, metadata, log structures, and de-duplication.
You will find key differences in the flash endurance of single-level cell (SLC), multi-level cell (MLC), and triple-level cell (TLC) architecture:
- SLC NAND flash can endure around 50,000 to 1,00,000 write cycles.
- MLC NAND flash can sustain up to 3,000 write cycles. eMLC or enterprise MLC version supports about 10,000 write cycles.
- TLC NAND Flash has low endurance and can take about 300 to 1,000 write cycles.
Learn more about the difference between SSD and HDD speeds.
How to Estimate How Long Your SSD Will Last
The lifespan of an SSD primarily depends upon the TBW and DWPD. Here’s how you can estimate how long the SSD will last:
TBW
The TBW is a measure of data the drive can write over its lifespan. For example, if an SSD has a 300 TBW rating, the drive can write 300 TB data before it needs replacement.
The Samsung 85 Pro series has SSDs of capacities: 128 GB, 256 GB, 512 GB, 1 TB, 2 TB, and 4 TB. It is built with 3D V-NAND and has a ten-year warranty.
The maximum TBW for a 25 GB SSD is 150. For 512 GB and 1 TB SSD capacity, the maximum TBW is 300. The 2 TB drive has 450 TBW capacity, and the 4 TB drive has 600 TBW capacity.
DWPD
The DWPD measures the number of times you can rewrite the entire SSD every day over its lifespan. For example, you can consider a 200 GB SSD drive with DWPD 1 and a warranty period of five years. It means that you can rewrite 200 GB daily for five years without chances of failure.
From this data, you can also calculate the TBW. As you can write 200 GB for 365 days for five years, the total TBW will be:
200*365*5= 365,000 GB, or 365 TB writes
Similarly, if the DPWD is 2 and the other factors remain the same, i.e., the SSD capacity is 200 GB and the warranty period is five years, you can estimate the TBW by:
2*200*365*5= 730,000 GB, or 730 TB writes
Calculation
To calculate the SSD lifespan, you can use the following formula:
(Write cycles * Capacity) / (SSD factor * Data Written per year)
Consider a Samsung 850 PRO, TLC SSD, with a capacity of 1 TB.
Then,
Write cycles= 3,000
Capacity= 1 TB or 1,000 GB
SSD Factor: real amount of data to actual amount of data written= 5 (consider)
Amount of data written to the drive per year= 1,500-2,000 GB (estimated)
Thus, the formula becomes:
(3,000 * 1,000)/(5 * 1,750)
= 342 years
The drive cannot be guaranteed to be relied upon for 342 years. But based on these assumptions, the oxide layer of the SSD will last this long.
Read more about the best and fastest SSDs.
Mean time between failures
The Mean time between failures (MTBF) is used popularly for HDDs to measure performance. However, they are not meaningful in the case of SSDs. MTBF is based on small sample sizes and is a statistical evaluation. It defines the average time between system breakouts. Thus, the asset is more reliable if the MTBF value is higher.
For an HDD, the MTBF is about half a million hours. It approximates 57 years. The average MTBF for SSDs is reported to be 2.5 million hours. It is less useful as there is no meaningful evidence.
So, when calculating the SSD lifespan, TBW and DWPD offer more practical results.
SSD Maintenance Best Practices
Even if SSDs are quite durable, they can show more errors than HDDs in less time. To improve the reliability and life cycle of these drives, manufacturers have come up with advanced technologies like:
Wear leveling
This method helps in the uniform distribution of the program/erase cycles over the entire memory block of the SSD. There are two types of wear leveling: dynamic and static.
Dynamic wear leveling algorithm ensures that the data programs and erase cycles are distributed uniformly throughout the NAND flash memory blocks. The dynamic algorithm gets executed whenever the data is written into the flash memory. Using a map, the LBAs (logical block addresses) from the operating system are linked to the physical flash memory. When the system has to rewrite data, a new block is linked. This helps SSDs last longer.
In the case of static wear leveling, the operating system also links LBAs to the physical memory using a map. In this case, unchanged blocks are irritated and replaced with written blocks.
Error Correction Code (ECC)
With Error Correction Code, the software can detect and correct bit errors. NAND flash commonly has these errors. Data may get corrupted as a result. ECC can also correct the bot errors caused due to the wearing out of memory cells. Thus, it can lengthen the lifetime of the memory blocks and increase the SSD lifespan.
Bad Block Management
This method helps detect bad blocks and prevents the system from writing data into these blocks. There are early bad blocks and later bad blocks in the NAND flash memory.The early bad blocks are unavoidable as they are created during the production process. Later bad blocks are created due to the repeated P/E cycles.
Bad Block Management uses the skip block method, which helps the controller jump to the next good block when encountering a bad one. In the reserve block method, the bad block is replaced using a reserved good one. Thus, bad block management extends the lifespan and reliability of SSDs.
TRIM
The TRIM command wipes deleted pages and blocks to contribute to longer SSD life and improve its performance. It helps erase the data blocks which are no longer in use. Thus, the storage can be efficiently managed as it directs the controller to discard invalid data pages.
Are SSDs More Dependable Than HDDs?
SSDs are faster, more compact, and more durable. They also consume less power. They can speed up performance. They are more used in enterprise environments. HDDs have increasing chances of mechanical failure and are more susceptible to damage.
But, HDDs are more affordable, and even in case of damage, data can be recovered easily. HDDs are preferable if you want to store large amounts of data and do not need to access it frequently. If you need a faster computing experience, SDDs will be more helpful. Thus, performance-wise, SSDs are more reliable.
Bottom Line: SSD Lifespan
There are no perfect storage devices, and it is always advisable to back up your data regularly to avoid any significant loss. Besides, SSDs have a better lifespan when compared to other devices; it also depends on how well you handle them. So, treat your SSD with great care to make them last longer.
Learn about trends driving the SSD market today.
