The complexity and scale of today’s cloud storage systems is growing fast. In response to these challenges, Software- Defined Storage (SDS) has recently become a prime candidate to simplify storage management in the cloud. This article presents IOStack: The first SDS architecture for object stores (OpenStack Swift). At the control plane, the provisioning of SDS services to tenants is made according to a set of policies managed via a high-level DSL. Policies may target storage automation and/or specific SLA objectives. At the data plane, policies define the enforcement of SDS services, namely filters, on a tenant’s requests. Moreover, IOStack is a framework to build a variety of filters, ranging from general-purpose computations close to ...