Flash memory continues to increase in popularity as the storage media of choice for business storage systems. Now “flash memory is an erase-before-write medium.” Unfortunately, “the erasure unit (called [a] block) is much larger than the write unit (called [a] page),” which means that “an entire block needs to be erased even if [only] a small portion [is changed]” (p. 12:2). That sets in motion a process to ensure the validity and reliability of the data where the actual data written to the physical storage media is a multiple of the logical amount of data that was requested to be written, that is, write amplification.

Reducing write amplification is important as it not only improves performance (fewer writes), but also protects the time that the storage can reliably operate without wearing out. The authors propose a technique whereby non-volatile memory (NVM), such as phase-change memory (PCM) or 3D XPoint, provides a persistent cache for flash storage. Their cooperative data management (CDM) scheme leads to the reduction of write amplification through the cooperative exploitation of the movement of data between flash memory and the NVM cache. The scheme takes advantage of the fact that due to its non-volatility, NVM can serve as the temporary home for the valid original data during the updating process. The paper goes on to discuss the details of how the CDM scheme reduces write amplification.

The paper should serve as a useful reference for those readers involved in the design and development of flash storage systems.