Can SQL Server be sharded for distributed data processing? Or are there any limitations that prevent relational databases from being sharded ?
SQL Server has a feature called "distributed federated views" or sometimes "partitioned views". (Confusingly, this is very different that the "partitioned tables" feature introduced in SQL Server 2005.)
The distributed federated views feature allows a crude, inflexible sort-of-sharding. It has been in the product since SQL Server 2000. I have never personally seen anyone use the feature and be happy with it. Here is a blog entry that covers the feature a bit:
In short, Microsoft does not provide easy-to-implement support for sharding in the box. You can always build your own sharding system that uses SQL as the storage layer. I would look through CodePlex and SourceForge before trying to write my own.
Sorry for the formatting, I'm on a phone.