In my previous post I mentioned that IIS Manager (more specifically Microsoft.Web.Administration) has two algorithms for assigning a Site ID when no ID is specified.
The two algorithms are:
In either case we will ensure that whatever ID we generate it will not collide with any existing Site.
These algorithms are configured using the following registry key:
In there you will find a DWORD attribute called IncrementalSiteIDCreation when set to 1 we will use the Incremental algorithm (1), otherwise we will use the Site name hash.
Bottom line if you really care about the Site ID and are provisioning the sites using Microsoft.Web.Administration you are better off having your own deterministsic algorithm for assigning the Site ID yourself and it will actually be considerably faster.
If you are using the UI chances are you really don't care about the Site ID, cause you would never have to interact with it (again might need changes when using certain ASP.NET features).