In this paper, we present the QuantCloud infrastructure, designed for performing big data analytics in modern quantitative finance. Through analyzing market observations, quantitative finance (QF) utilizes mathematical models to search for subtle patterns and inefficiencies in financial markets to improve prospective profits. To discover profitable signals in anticipation of volatile trading patterns amid a global market, analytics are carried out on Exabyte-scale market metadata with a complex process in pursuit of a microsecond or even a nanosecond of data processing advantage. This objective motivates the development of innovative tools to address challenges for handling high volume, velocity, and variety investment instruments. Inspired by this need, we developed QuantCloud by employing large-scale SSD-backed datastore, various parallel processing algorithms, and portability in Cloud computing. QuantCloud bridges the gap between model computing techniques and financial data-driven research. The large volume of market data is structured in an SSD-backed datastore, and a daemon reacts to provide the Data-on-Demand services. Multiple client services process user requests in a parallel mode and query on-demand datasets from the datastore through Internet connections. We benchmark QuantCloud performance on a 40-core, 1TB-memory computer and a 5-TB SSD-backed datastore. We use NYSE TAQ data from the fourth quarter of 2014 as our market data. The results indicate data-access application latency as low as 3.6 nanoseconds per message, sustained throughput for parallel data processing as high as 74 million messages per second, and completion of 11 petabyte-level data analytics within 53 minutes. Our results demonstrate that the aggregated contributions of our infrastructure, parallel algorithms, and sophisticated implementations offer the algorithmic trading and financial engineering community new hope and numeric insights for their research and development.