You need to plan the amount of database space to dedicate to user document storage.
As an example, these factors can be combined in a simple formula to provide a rough assessment of the storage requirement: Ns*((Dr*Zr)+Za+(Dp*Zp))+Ng*Zg
You also need to plan the database-serving capacity as a function of Input/Output instructions per second (IOPS). To size your I/O serving capacity requirement, you need to determine the workload capacity for each disk in the array that supports the IBM® XDMS database.
Assume that each 15K RPM disk in the array can sustain 120 IOPS. Use this rate combined with the expected workload on the database to derive the number and types of disks you will need to support the database. Information about the relationship of number of XML Configuration Access Protocol (XCAP) requests to I/O requests for typical workloads is documented in the Capacity Planning Guide, which you can obtain from the IBM Support Web site.
You can also configure IBM XDMS to generate usage records (audit/billing records) for all activity that it processes. You should plan for enough database capacity to handle the expected billing traffic within the limits and constraints imposed by your usage record processing policy (archival, extraction, and so forth). More details and recommendations are available in the Capacity Planning Guide.