Wear leveling

Wear leveling (also written as wear levelling) is a technique[1] for prolonging the service life of some kinds of erasable computer storage media, such as flash memory, which is used in solid-state drives (SSDs) and USB flash drives, and phase-change memory.

The idea underpinning wear leveling is similar to changing position of car tires, avoiding repetitive load from being used on the same wheel.

The term preemptive wear leveling (PWL) has been used by Western Digital to describe their preservation technique used on hard disk drives (HDDs) designed for storing audio and video data.

Wear leveling attempts to work around these limitations by arranging data so that erasures and re-writes are distributed evenly across the medium.

In this way, no single erase block prematurely fails due to a high concentration of write cycles.

[6][7] Conventional file systems such as FAT, UFS, HFS/HFS+, EXT, and NTFS were originally designed for magnetic disks and as such rewrite many of their data structures (such as their directories) repeatedly to the same area.

Global wear leveling addresses this problem by managing all blocks from all chips in the flash memory together―in a single pool.

A view on stairs, where the central part deteriorated from people using mostly the middle section of each step.
The central section of stairs worn out from pedestrian traffic constrained to the middle.
A fragment of a road surface, heavily rutted by car wheels following the same path.
Deep ruts from car wheels following the same path.