This week, Boston-based startup ClearSky Data came out of stealth with a tiered approach to cloud storage that differentially stores hot, medium and cold customer storage to optimize cost and recognize gradations in the frequency with which data storage is used by customers. ClearSky Data leverages a three tiered storage infrastructure that keeps most important, frequently used data on premise whereas the second tier uses a colocation facility enabled by means of a collaboration with Digital Realty. The Digital Realty colocation facility in question is based within a 120 mile radius of each customer. The third storage tier is composed of Amazon Web Services for data not often accessed by customers. One of the salient advantages of ClearSky is that it gives customers the low latency required for production-grade workloads. Backed by General Catalyst and Highland Capital, ClearSky Data has raised $12M to date.