If you are using SQL Server on premise today and want to move your database to SQL Azure on the cloud, the first questions you need to get answered are:
“Which service tier and performance level should I use?”
“How many database throughput units(DTUs) do I need?”
“And what is this DTU actually?”
These questions are not that easy to answer as the performance characteristics of your SQL Server on premise are different from SQL Azure.
Let’s first answer the question what is a DTU:
A DTU is a unit of measure of the resources that are guaranteed to be available to a standalone Azure SQL database at a specific performance level within a standalone database service tier. A DTU is a blended measure of CPU, memory, and data I/O and transaction log I/O in a ratio determined by an OLTP benchmark workload designed to be typical of real-world OLTP workloads.
Source: https://azure.microsoft.com/en-us/documentation/articles/sql-database-what-is-a-dtu/
OK, so a DTU is one number combining a certain amount of CPU power, memory and I/O. That brings us to the next question, how many DTUs do I need?
To answer this question we can call in help from the Azure SQL Database DTU calculator. This website offers a free tool that helps you capture some performance metrics of you current on-premise environment. The result can be uploaded to the website and you can see how the database resource consumption matches fits within the limits of each Service Tier/Performance Level.
Great help!