This series is a simplified version of the implementation on how to capture contact data from an external non-Sitecore site and import into xDB.
Emer's Blog
My Sitecore adventures
In part 3 of this blog series I will go through steps to capture available contact data from any non-Sitecore site.
Sitecore xDB - Capturing Contact Data from non-Sitecore Site - Part 4 - Import Captured Contact Data
In part 4 of my blog series on how to capture contact data from a non-Sitecore site I will discuss different options to import captured contact data into Sitecore xDB.
By default, Sitecore is installed with 2 shard databases, shard0 and shard1. This is ok and generally acceptable for smaller sites where you won't see large traffic and interaction numbers however, using only 2 shard databases can become a serious bottleneck in high performing sites.