Programming an SSD Controller to Support Batched Writes for Variable-Size Pages

Abstract

Exploiting a storage hierarchy is critical to cost-effective data management. However, most systems are challenged when data is not in cache because of the additional I/O to move data between SSD and main memory. To improve both cost and performance, some systems use a log structured store to write a batch of pages instead of a "block-at-a-time". However, host-based log structuring incurs the additional cost and complexity of garbage collection and recovery, duplicating similar SSD FTL functionality. In prior work, we presented a customized SSD controller implementation for an Open-Channel SSD to enable host computers to write batches of fixed size pages. This current work is a major redesign to support a batched write interface with variable size pages. Variable size pages can enable easy support of data compression and encryption, as well as reducing internal page storage fragmentation, e.g, within a B-tree. Thus it further improves I/O performance while making it easier and more efficient to support these capabilities.