Just after posting about this excellent Database.com and SQL Azure comparison, I have found another interesting Microsoft Azure article.
It is about Sharding with SQL Azure and is covering aspects as principles, challenges, and common patterns for horizontal partitioning, a high level design of an ADO.NET sharding library, and an intro to SQL Azure Federations:
The proposed implementation will map data to specific shards by applying one or more strategies upon a “sharding key” which is the primary key in one of the data entities. Related data entities are then clustered into a related set based upon the shared shard key and this unit is referred to as an atomic unit. All records in an atomic unit are always stored in the same shard.
Be aware that the article is quite long, but definitely worth reading.
Original title and link: Sharding with SQL Azure (NoSQL databases © myNoSQL)