Here is some great information via MitchP on the number and characteristics of SharePoint including their availability supported models (mirroring, etc.)
Example of content for the config db:
The configuration database contains data about SharePoint databases, Internet Information Services (IIS) Web sites, Web applications, trusted solutions, Web Part packages, site templates, and Web application and farm settings specific to SharePoint 2010 Products, such as default quota settings and blocked file types.
Default database name prefix when installed by using the SharePoint Products Configuration Wizard
General size information and growth factors
However, transaction log files are likely to become large. For more information, see Additional notes, below.
Recommended scaling method
Must scale up; that is, the database must grow larger, because only one configuration database is supported per farm. (Significant growth is unlikely.)
Associated health rules
Supported backup mechanisms
SharePoint Server 2010 backup and recovery, SQL Server, and System Center Data Protection Manager (DPM) 2010. The configuration database is a special case for backup and recovery. For more information, see Additional notes below.
Default recovery model
Full. We recommend that you switch the configuration database to the simple recovery model to restrict growth of the log file.
Supports mirroring within a farm for availability
Supports asynchronous mirroring or log-shipping to another farm for disaster recovery