Managing virtual storage systems: an approach using dependency analysis

We present an approach for managing the performance of virtual storage systems by experimentally identifying the dependencies that exist between various components that comprise the system. Specifically, we show how one may profile dependencies between each logical volume exported by a storage system and components that this volume uses. To do so the technique estimates the arrival rate and size of requests issued to the internal system component as a functions of arrival rate and size of requests issued to the logical volume. The complete dependency profile of the system consists of a set of such functions for READ and WRITE operations separately and for each pair: logical volume - internal system component. The empirical technique of obtaining such profiles for typical existing storage systems is presented. We propose the use of Common Information Model (CIM) as a way to express dependency and performance information in an architecture-independent manner. The dependencies between components are computed as a fraction of bandwidth that is passed on to the sub-components. We discuss how the dependency profile of the system may be used to perform root-cause analysis and early Service Level Agreement violation notification. We also demonstrate the use of the method by applying it to a Linux system using software RAID.