Single cluster architecture
In clustered architecture utilizes the same user customization, community and release data throughout an environment, any user customization made against one portal cluster member by a user would be available to the same user as and when that user accesses any of the other cluster members participating in the same portal cluster.
Multiple cluster architecture
Release data is all portal content definition, rules and rights such as Page Hierarchy, available portlets and themes, Templates, Credential slots, Portal personalization rules and policies
In setup that consist of multiple lines of production one copy of release data exists per cluster. Administrator must make sure that the content of the release database is consistent across the different lines, in particular after modification of the release data on the production line
Customization data is the the data associated with single user. It has data such as private pages or any customizations done by user. This data cannot be shared by mulitple users.
In a setup that consists of mulitple lines of production, customization data is kept in a database that is shared across the lines of production. Therefore data is automatically in sync across the lines of production.
Community data: is all resources that are typically modified during production such as shared documents or application resources. Typically users and groups are allowed to modify or delete shared resources.
In a setup that consist of multiple lines of productions, community data is kept in a database that is shared across the lines of productions. Therefore data is automatically in sync across the lines of productions.