How does wear leveling work in SSDs?

Wear levelling in SSDs works by distributing data evenly across all physical blocks to prevent premature wear out.

Solid State Drives (SSDs) use a technique called wear levelling to extend their lifespan. This is necessary because the flash memory cells in an SSD have a limited number of write cycles before they can no longer reliably store data. If data were continually written and rewritten to the same cells, those cells would wear out more quickly than others, reducing the overall lifespan of the drive.

Wear levelling works by ensuring that data is written to different physical blocks each time, rather than repeatedly using the same ones. This spreads the wear and tear across all the cells in the drive, rather than concentrating it in a few areas. There are two main types of wear levelling used in SSDs: dynamic and static.

Dynamic wear levelling works by writing new data to the least used blocks first. This helps to ensure that all blocks get used evenly. However, it doesn't take into account data that is rarely or never rewritten. This is where static wear levelling comes in.

Static wear levelling also writes new data to the least used blocks, but it periodically moves data from heavily used blocks to less used ones, even if that data hasn't been rewritten recently. This ensures that all blocks, including those containing rarely changed data, are used evenly.

The wear levelling process is managed by the SSD's controller, which keeps track of how many times each block has been written to. This information is used to determine which blocks to write to next, and when to move data for static wear levelling.

In summary, wear levelling is a crucial technique used in SSDs to distribute data evenly across all physical blocks. This prevents any single block from wearing out prematurely, thereby extending the overall lifespan of the drive. It's a complex process, but one that's essential for the reliable operation of SSDs.