The task of deploying a software stack as a VM image onto a virtualized server has historically been a highly labor-intensive task. For instance, one has to first deploy and configure the OS along with all requisite patches. After that, the administrator has to install and configure the application server and all its constituent components (e.g. HTTP server, etc.) as well as patches and other fixes. For applications requiring a database, that becomes yet another piece of middleware that needs to be installed and configured. Then there is the application itself. Collectively, deploying and testing a complete application manually can require days or weeks to accomplish depending upon its overall complexity. In a private cloud environment, this kind of turnaround is untenable. The IBM Workload Deployer is specifically designed to address this problem. To the right is a screenshot of the pattern designer for IWD.
Following the IBM lead, Oracle is now starting to move in a similar direction. In June 2010 Oracle announced the Oracle Virtual Assembly Builder. This product provides provisioning of the virtual appliances into the Oracle VM environment. Other than overall lack of product maturity, there are number of significant limitations with the current version of the Oracle Virtual Assembly Builder product. Read full comparison in this blog entry: Comparison of two private cloud tools from IBM and Oracle.
When Oracle ships new version of the OVAB product, I will update my comparison, but for now this is the best I can do given current versions of both products.