How does wear levelling extend the life of a SSD?

In a previous blog, we looked at some of the most basic technologies that make SSDs and their Flash NAND chips work more efficiently and thus live longer. But there is one thing we have not discussed: wear levelling.

What is wear levelling?

Without wear levelling, a Solid State Drive would never reach its optimal lifespan. Since an SSD consists of many Flash NAND cells and each of them is only capable of a certain amount of read-/write- operations, an SSD would normally fail without wear levelling much quicker than with this technology.

This is because technology is based on algorithms that make sure that each Flash NAND storage cells are used equally. A cell can only handle 3000 – 100,000 read-/write cycles. But even this high amount of cycles can be reached relatively soon.

Wear levelling in more detail

Without wear levelling algorithms, the flash controller must permanently assign the logical addresses from the operating system to the physical addresses of the Flash memory. That means that every new write to a previously written block must first be read, erased, modified and re-written to the first location. Not only is this approach highly time-consuming, but it also means that some storage spaces will be used more frequently than others and wear out faster. When a few blocks reach their end of life, the device can become inoperable and data loss is likely to occur.

Wear levelling algorithms

By using wear levelling algorithms the Solid State Drive controller distributes the write operations in such a way that all NAND memory cells are written to equally. There are two different ways this is accomplished: static wear levelling and dynamic and static wear levelling.

Simply put, dynamic wear levelling means that the SSD controller takes the least used free flash blocks to write data to. Even though this method is a little bit better than no wear levelling at all, when a lot of data is stored on a SSD the cells still wear out more quickly. That is why (hopefully) an additional method is used - static wear levelling. This method helps to reduce the wear of the flash cells over the entire capacity of the built-in FLASH chips by shifting the data to less used flash blocks.

Conclusion

Wear levelling is one of the most essential technologies to expand the lifetime of an SSD. Therefore when buying a new SSD it is essential that you choose one where both methods of wear levelling – dynamic and static – are implemented in the firmware. By doing so, you not only choose a product with a better life expectancy but also invest in data security. When both wear levelling methods are used, the more unlikely a data loss due to hardware failure will occur.

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