Abstract

Storage systems rely on maintenance tasks, such as backup and layout optimization, to ensure data availability and good performance. These tasks access large amounts of data and can significantly impact foreground applications. We argue that storage maintenance can be performed more efficiently by prioritizing processing of data that is currently cached in memory. Data can be cached either due to other maintenance tasks requesting it previously, or due to overlapping foreground I/O activity.

We present Duet, a framework that provides notifications about page-level events to maintenance tasks, such as a page being added or modified in memory. Tasks use these events as hints to opportunistically process cached data. We show that tasks using Duet can complete maintenance work more efficiently because they perform fewer I/O operations. The I/O reduction depends on the amount of data overlap with other maintenance tasks and foreground applications. Consequently, Duet’s efficiency increases with additional tasks because opportunities for synergy appear more often.

This work appeared at SOSP ’15 in October.