Contemporary datacenters house tens of thousands of servers. The servers are closely monitored for operating conditions and utilizations by collecting their performance data (e.g., CPU utilization). In this paper, we show that existing database and file-system solutions are not suitable for warehousing performance data collected from a large number of servers because of the scale and the complexity of performance data. We describe the design and implementation of DataGarage, a performance data warehousing system that we have developed at Microsoft. DataGarage is a hybrid solution that combines benefits of DBMSs, file-systems, and MapReduce systems to address unique challenges of warehousing performance data. We describe how DataGarage allows efficient storage and analysis of years of historical performance data collected from many tens of thousands of servers—on commodity servers. We also report DataGarage’s performance with a real dataset and a 32node, 256-core shared-nothing cluster and our experience of using DataGarage at Microsoft for the last one year.