The continuous growth of data centers prompts research into their energy impact. While some cloud providers give an overall estimate of data centers energy efficiency, there is a lack of transparency about data for individual components and functions. We explore metrics to evaluate the energy efficiency of cloud data storage in particular and represent them as Key Performance Indicators (KPIs) for organizational monitoring. To this aim, we perform an exploratory study with Schuberg Philis (SBP), a leading IT provider in the Netherlands to explore sustainability monitoring for cloud data storage. We identify the data provided by a cloud provider and explore the corresponding metrics in the academic literature. Based on the SBP’s sustainability roadmap, we propose three KPIs that are developed using an existing KPI framework. These KPIs are reviewed by the experts at SBP for their correctness and added value. The study provides, (i) an overview of the energy efficiency of cloud data storage, (ii) suggested KPIs to monitor and optimize the cloud data storage to meet the SBP’s sustainability goals. The KPIs are energy consumption (kW/h), storage capacity utilization (%), and capacity per watt (GB/Watt), and (iii) actions per KPI to reach the sustainability targets. The results of the study provide insights into monitoring the energy efficiency of data storage for SBP for potential optimization while building a foundation for developing similar approaches for other practitioners and for targeting sustainability concerns.