Isotope: ACID Transactions for Block Storage.

Existing storage stacks are top heavy and expect little from block storage. As a result, new high-level storage abstractions—and new designs for existing abstractions—are difficult to realize, requiring developers to implement from scratch complex functionality such as failure atomicity and fine-grained concurrency control. In this article, we argue that pushing transactional isolation into the block store (in addition to atomicity and durability) is both viable and broadly useful, resulting in simpler high-level storage systems that provide strong semantics without sacrificing performance. We present Isotope, a new block store that supports ACID transactions over block reads and writes. Internally, Isotope uses a new multiversion concurrency control protocol that exploits fine-grained, subblock parallelism in workloads and offers both strict serializability and snapshot isolation guarantees. We implemented several high-level storage systems over Isotope, including two key-value stores that implement the LevelDB API over a hash table and B-tree, respectively, and a POSIX file system. We show that Isotope’s block-level transactions enable systems that are simple (100s of lines of code), robust (i.e., providing ACID guarantees), and fast (e.g., 415MB/s for random file writes). We also show that these systems can be composed using Isotope, providing applications with transactions across different high-level constructs such as files, directories, and key-value pairs.