Use of write allocation decisions to achieve desired levels of wear across a set of redundant solid-state memory devices

Abstract

Redundant solid-state memory devices are used to enhance the operation of a network storage system. To reduce the likelihood of substantially concurrent failure of two or more such memory devices, write allocation decisions are made so as to influence the wear on the various solid-state memory devices, so that not all of the solid-state memory devices wear out at the same rate. This can be accomplished by skewing the wear caused by erases/writes, across the solid-state memory devices, so that the devices experience unequal wear and, therefore, do not all fail at or approximately at the same time. The roles of the various flash devices are adjusted when a solid-state memory device is replaced, such that subsequent write allocation decisions are based on the maintenance history (e.g., replacement history) of the devices as well as the past write history.