Variability of NVM response time and its effect on the performance of consumer SSDs

Solid-State Drives (SSDs) use non-volatile memories (NVM) for storing and retrieving information in the form of sectors and/or pages. For achieving high capacity, consumer SSDs use high density multi-level cells (MLC) memories that experience high read and write times. The maximum achieved I/O performance and the minimum response time depends on the used NVM technology, which determines the read and write times, and other system parameters, like the number of simultaneously accessed NVM channels, the SSD controller architecture, its functionality, the supported commands and the applied workload. Most of these parameters remain unchanged during the lifetime of an SSD, except for the read and write times which vary as the lifetime of the device progresses and higher variability is observed. By defining the basic equations of the maximum SSD performance and using experimental results, we determine how the increase of the NVM response time affects the performance of a consumer SSD and under what conditions this is observed by the SSD´s user.