Wearleveling

Wear leveling is a technique used to extend the lifespan of non-volatile memory, particularly NAND flash, by distributing erase and write cycles evenly across all memory blocks. Flash memory has a limited number of program/erase cycles per block, so concentrating writes on a subset of blocks accelerates wear and can cause early device failure. Wear leveling aims to prevent hotspots and thereby increase endurance and reliability.

In devices such as solid-state drives, a flash translation layer (FTL) separates logical addresses from physical storage locations. The FTL maintains metadata about the wear of blocks and determines where to place new or updated data. Dynamic wear leveling writes data to the least-worn blocks, updating the logical-to-physical mapping as needed. Static wear leveling, by contrast, occasionally relocates blocks that contain static (rarely rewritten) data to blocks with lower wear, so even idle data eventually wears evenly rather than leaving some blocks unused while others wear out.

Wear leveling can operate at different granularities, commonly block-level or page-level, and may be implemented with varying strategies from simple round-robin or greedy approaches to more sophisticated counters and heuristics. Garbage collection processes reclaim invalid pages and erase blocks to provide fresh space, but this activity interacts with wear leveling and can introduce write amplification and performance overhead.

Applications and limitations: wear leveling is a fundamental feature of flash-based storage devices, including SSDs, USB flash drives, and memory cards. While it reduces the risk of premature block failure and improves endurance, it does not eliminate wear entirely. Its effectiveness depends on workload patterns, data locality, and the efficiency of the FTL algorithm, and there is an ongoing balance between endurance, performance, and storage capacity.